SE545906C2

SE545906C2 - Hand-held percussive tool

Info

Publication number: SE545906C2
Application number: SE2230406A
Authority: SE
Inventors: Johan Nåsell
Original assignee: Atlas Copco Ind Technique Ab
Priority date: 2022-12-09
Filing date: 2022-12-09
Publication date: 2024-03-12
Also published as: SE2230406A1

Abstract

The present specification relates to a hand-held percussive tool (1) comprising a housing (10), and a pneumatic percussive mechanism (20) located in the housing and having an anvil (21) and a percussion piston (22) for impacting the anvil, wherein said piston is movably arranged along a longitudinal axis in a cylinder chamber (11) in said housing, said cylinder chamber being fluidly connected to a compressed air reservoir and wherein said anvil is arranged in said cylinder to be impacted by said piston, wherein said tool is further adapted to receive a chisel (30) to extend at a front end (la) of the tool and on which said piston acts via said anvil; and wherein said tool further comprises a spring element (40) arranged to act between said housing and said chisel to, in use, counteract forward movement of said housing with respect to said chisel.

Description

Technical field The present invention generally relates to hand-held percussive tools, also known as. hand-held pneumatic impact tools.

Technical Background Pneumatic impact tools, where examples include so called chipping hammers, chisel- or impact hammers, are known to be used for example for material removal. Such tools, also known as percussive tools, percussion tools and pneumatic impact tools - all terms will be used interchangeably throughout the present specification, normally comprise a piston brought to reciprocate in a cylinder ofthe tool by means of compressed air allowed to ﬂow through inlets and outlets in the cylinder and arranged to impact a tool attachment, e.g. a hammer or chisel, often via a so called anvil.

The use and operation of such tools is often associated with vibrations due to the percussive operation provided where sufficient amounts of energy must be transferred to the tool attachment in order to provide efficient and fast material removal. Such vibrations, if too high, may be harmful to the operator. ln order to provide low vibrations and high efficiency, the housing and chisel must be positioned correctly with respect to one another. This since particularly severe vibrations arise if the chisel impacts the housing during use. To control the level of vibration, the operator of the tool must carefully adapt the position of the tool housing with respect to the chisel or hammer in order to avoid any contact between the chisel and housing which would cause undesired vibrations which will be transmitted to the user. The length over which the chisel may reciprocate without contacting the housing and/or other structures in the tool, i.e. where the chisel may move freely or ﬂoat, may be referred to as the ﬂoating length.

To keep the chisel within the ﬂoating length is however not easy since the user has little or no possibility to determine the exact relative position ofthe housing and chisel, and the resulting behavior ofthe tool in terms of vibrations is thus largely dependent on the skills and experience of the user operating the tool.

Hence, there exists a need for improvement in the field of design of handheld percussive tools.

Summary of the invention Accordingly, it would be desirable to provide a percussive tool were vibrations levels are reduced. ln particular, it would be desirable to provide such a tool providing improved handling and usability. To better address one or more ofthese concerns a hand-held percussive tool as defined in the independent claim is provided, preferred embodiments are defined in the dependent claims.

According to a first aspect of the invention a hand-held percussive tool is provided, the tool comprising a housing and a pneumatic percussive mechanism located in the housing and having an anvil and a percussion piston for impacting the anvil. Wherein the piston is movably arranged along a longitudinal axis in a cylinder chamber in the housing, the cylinder chamber being ﬂuidly connected to a compressed air reservoir, wherein the anvil is arranged in the cylinder to be impacted by the piston, wherein the tool is further adapted to receive a chisel to extend at a front end ofthe tool and on which the piston acts via the anvil and wherein the tool further comprises a spring element arranged to act between the housing and the chisel to, in use, counteract forward movement of the housing with respect to the chisel.

According to the first aspect, the percussive tool provides an inventive solution to the concerns described above by means of a design incorporating a spring element arranged to counteract a forward movement of the housing with respect to the chisel. Hereby the user is provided with additional feedback regarding the actual position of the housing with respect to the chisel. This by means ofthe introduction of a spring force, which is added to the force arising due to the driving air pressure which has to be overcome by the user to position the housing correctly with respect to the chisel. This spring force increases over length, i.e. with increased displacement, as opposed to the force needed to overcome the air pressure which is constant. Hereby, a force feedback is provided to the user greatly facilitating the task of maintaining the chisel in the ﬂoating position, i.e. within the so called ﬂoating length, thus making it much easier to avoid vibrations and forces due to the chisel undesirably hitting the housing. ln other words, the spring may be described as arranged to counteract forward movement ofthe housing with respect to the chisel when said power tool housing, in use, is pushed forward with respect to said chisel. Hereby, the spring element increases the force needed when pushing the tool forward and the force which the operator has to overcome or counteract becomes not only larger than the constant force arising from the driving air pressure alone, but also varying depending on the relative distance between housing and chisel. Without a spring element, the force required throughout the ﬂoating length is constant, since the force in this case is only dependent on the driving air pressure.

The user thus needs to apply a force equal to the sum ofthe force from pressure in driving air chamber and the force from the spring element to hold the tool in position - i.e. within the ﬂoating length, and further an increasing force with increasing displacement, and is thus given feedback of the relative position.

The stiffness ofthe spring element is preferably adapted such that a user receives sufficient feedback, but not too large to avoid a too large increase of the reaction forces.

According to one embodiment, the forward movement is counteracted by means of a compression ofthe spring element. As the spring element is compressed, the additional force arises which provides feedback as it has to be overcome by the user.

According to one embodiment, the spring element has a linear stiffness. Hereby, a linearly rising force providing feedback is achieved as the spring element deforms.

According to one embodiment, the housing further comprises a shoulder formed in an inner surface ofthe housing, wherein the spring element acts between the shoulder and the chisel. The shoulder may be formed in an inner surface of the cylinder, or cylinder chamber. ln one embodiment, the housing and/or cylinder or cylinder chamber comprises a distal end wall arranged at a forward end ofthe tool. The end wall may comprise an opening through which the chisel may extend. ln other embodiments, the percussive tool may comprise a separate inner structure arranged at or near the front end of the tool to stop the chisel from moving too far in a forward direction. ln one embodiment, the ﬂoating length is defined between (and/or delimited by) the shoulder and the end wall - i.e. the chisel should in such an embodiment move between the shoulder and end wall but not make contact with the shoulder or end wall.

According to one embodiment, the chisel comprises a shoulder formed in an outer surface thereof, wherein the spring element acts between the shoulder and the housing. The shoulder may in some embodiments be described as an annular protrusion on a shaft ofthe chisel. The shoulder may be utilized to stop the chisel for limiting the motion ofthe chisel with respect to the housing, e.g. from leaving the housing. ln some embodiments, ﬂoating length refers to the distance over which the shoulder formed in the chisel may move before hitting the housing, or reciprocate before hitting a respective adjacent portion of the housing.

The chisel shoulder may have a diameter larger than the diameter of the central opening in the housing end wall.

According to one embodiment, the spring element acts between the shoulder formed in the housing and the shoulder formed in the chisel. ln such an embodiment, the side of the shoulder facing the piston and anvil (i.e. the rear side) may comprise a spring seat.

The spring element may hence in some embodiments be arranged to act between a shoulder formed in an inner surface ofthe housing and/or cylinder.

According to one embodiment, the tool further comprises an intermediate element arranged on the chisel, wherein the spring acts between the intermediate element and the housing. The intermediate element may comprise a spring seat. The intermediate element may further in some embodiment be arranged on a shoulder, or annular protrusion, formed in the chisel. The intermediate element may be arranged on the shaft by means of a press or shrink fit or similar or it may be loosely fitted on the shaft. According to one embodiment, the intermediate element is made from rubber or plastic.

According to one embodiment, the hand-held percussive tool further comprises a chisel guide through which a rear portion of said chisel extends. The chisel guide may be arranged to guide the longitudinal movement of the chisel and/or lock the rotation of the chisel. ln some embodiments, the chisel guide defines a stop against which the shoulder ofthe chisel and/or the intermediate element bears at an end- or turning position.

According to one embodiment, the spring element is a coil spring. ln some embodiments, the spring element is a compression coil spring. ln other embodiments, the spring element is a spring element chosen from the group comprising a coil spring, a wave spring and a disc spring.

According to one embodiment, the spring stiffness lies in the range 5-15 N/mm. ln some embodiments in the range 7-12 N/mm. ln one embodiment, the spring stiffness is chosen such that a desired increase of force is achieved corresponding to a fraction of the pneumatic feed force. The stiffness may in such an embodiment be chosen such that the force increase lies in the range 5-25% ofthe pneumatic feed force, in some embodiments 10-15%.

According to one embodiment, the piston is driven by said compressed air reservoir via a pneumatic cylinder arrangement. ln one embodiment, the cylinder arrangement comprises a driving air chamber 71 and a return pressure chamber 72. The cylinder arrangement may further for example be such that the air pressure is provided by a driving air chamber into which a piston shaft extends.

According to one embodiment, the tool is a pneumatic chipping hammer. According to one embodiment, the tool is a pneumatic scaler.

Further objectives of, features of and advantages of the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art realize that different features ofthe present invention can be combined to create embodiments other than those described in the following.

Brief description of the drawings The invention will be described in the following illustrative and non-limiting detailed description of exemplary embodiments, with reference to the appended drawing, on which Figure 1 is a perspective exploded view of an exemplary percussive tool according to one embodiment.

Figure 2 is a cross sectional view of a portion of an exemplary percussive tool according to one embodiment. Figure 3 is a schematic illustration of a percussive tool according to one embodiment.

All figures are schematic, not necessarily to scale and generally only show parts which are necessary in order to elucidate the invention, wherein other parts may be omitted or merely suggested.

Detailed description An exemplary hand-held percussive tool 1 is shown in figure 1, in the illustrated case a pneumatic chipping hammer, comprising a housing 10 and a pneumatic percussive mechanism 20 located in the housing. ln the illustrated embodiment, the housingincludes the outer parts of the tool not involved in the percussive motion ofthe tool.

The percussive tool is adapted to receive a chisel at a front end 1a and further comprises a connection 11a arranged at a rear end 1b of the tool for providing a connection to a compressed air reservoir.

The percussive mechanism 20 according to an exemplary embodiment of the tool is shown in fig. 2 in greater detail.

The pneumatic percussion mechanism 20 comprises an anvil 21 and a percussion piston 22 for impacting the anvil. The piston 22 is movably arranged along a longitudinal axis A-A in a cylinder chamber 11 in the housing 10. The cylinder chamber 11 is in turn ﬂuidly connected to a compressed air reservoir.

The anvil 21 is arranged in the cylinder chamber 11 to be impacted by the piston 22. The anvil 22 in turn acts on a rear portion 32 of the shaft of a chisel 30, which chisel extends at a front end 1a of the tool.

As may be seen from fig. 2, a spring element 40 is arranged to act between the housing and the chisel 30 to, in use, counteract forward movement ofthe housing 10 with respect to the chisel 30. Further, a chisel guide 60 is provided through which a rear portion 32 ofthe chisel extends. ln the illustrated embodiment, a compressive coil spring 40 acts between a shoulder 12 formed in the housing 10 and an intermediate element 50 arranged on a shoulder or annular protrusion 31 formed on the chisel ln use, as the forward end 30a ofthe chisel 30 bears against a work piece, forward movement ofthe housing 10 with respect to the chisel 30 is hence counteracted by a compression ofthe coil spring The functionality of the percussive mechanism will now be described with reference to an embodiment schematically illustrated in fig.

The illustrated tool comprises an anvil 21 arranged in the cylinder chamber 11 to be impacted by the piston 22 driven by said compressed air reservoir via a pneumatic cylinder arrangement 70, in the illustrated embodiment comprising a driving air chamber 71 and a return pressure chamber 72. The anvil 22 in turn acts on the chisel 30. A spring element 40 is arranged to act between the housing 10 and the chisel 30 to, in use, counteract forward movement of the housing 10 with respect to the chisel To work with low vibration and high performance, the housing and chisel must be positioned correctly with respect to one another. More particularly, the chisel should move within the ﬂoating length FL - i.e. where the piston only hits the chisel and the chisel is freely moving within the housing. The ﬂoating length is schematically illustrated by the dashed line FL in fig. ln use, as the forward end 30a ofthe chisel bears against a work piece, the user applies a force to the housing 10 in a forward direction to position the housing correctly with respect to the chisel.

Without the spring 40, the force required would be constant over the ﬂoating length since the force which the user has to overcome or counteract in such a case is only dependent on the pressure in the driving air chamber 50. However, by means of the introduction ofthe spring element 40, a force which changes as the housing is pushed forward with respect to the chisel is added.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiment. The skilled person understands that many modifications, variations and alterations are conceivable within the scope as defined in the appended claims. Additionally, variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, form a study of the drawings, the disclosure and the appended claims. ln the claims, the word “comprising" does not exclude other elements or steps and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination ofthese measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope ofthe claims.

Claims

1. Hand-held percussive tool (1) comprising: a housing (10), and a pneumatic percussive mechanism (20) located in the housing and having an anvil (21) and a percussion piston (22) for impacting the anvil, wherein said piston is movably arranged along a longitudinal axis in a cylinder chamber (11) in said housing, said cylinder chamber being ﬂuidly connected to a compressed air reservoir and wherein said anvil is arranged in said cylinder to be impacted by said piston, wherein said tool is further adapted to receive a chisel (30) to extend at a front end (1a) ofthe tool and on which said piston acts via said anvil; and wherein said tool further comprises a spring element (40) arranged to act between said housing and said chisel to, in use, counteract forward movement of said housing with respect to said chisel.

2. Hand-held percussive tool according to claim 1, wherein said forward movement is counteracted by means of a compression of said spring element

3. Hand-held percussive tool according to any one ofthe preceding claims, wherein said spring element has a linear stiffness.

4. Hand-held percussive tool according to any one ofthe preceding claims, wherein said housing further comprises a shoulder (12) formed in an inner surface of said housing, and wherein said spring element and said chisel between said shouldermå;

5. Hand-held percussive tool according to any one of the preceding claims, wherein said chisel has a shoulder (31) formed in an outer surface thereof and wherein said spring element acts between said shoulder and said housing

Hand-held percussive tool according to claim 4 and 5, wherein said spring element acts between said shoulder formed in said housing and said shoulder formed in said chisel.

Hand-held percussive tool according to any one ofthe preceding clajims, further comprising an intermediate element (50) arranged on said chisel, wherein said spring acts between said intermediate element and said housing.

Hand-held percussive tool according to claim 7, wherein said intermediate elemen is made from rubber or plastic.

Hand-held percussive tool according to any one ofthe preceding cla_š_ms, further comprising a chisel guide (60) through which a rear portion (32) of extends. said chisel»

Hand-held percussive tool according to any one ofthe preceding cla§_ms, e :Vwherein said spring elementi ~ is a spring element chosen from the group comprising a coil spring, a wave spring and a disc spring.

Hand-held percussive tool according to claim 10, wherein the spring stiffness lies in the range 5-15 N/mm.

Hand-held percussive tool according to any one ofthe preceding cla§_ms, »is driven by said compressed air reservoir via a wherein said piston pneumatic cylinder arrangement (70).

Hand-held percussive tool according to any one ofthe preceding claims, wherein said tool jpšspišvis a pneumatic chipping hammer.

14. Hand-held percussive tool according to any one of the preceding c1aims wherein said tool a pneumatic scaler.