Powered hammer with a vibration dampening mechanism

A powered hammer is described comprising a housing, a tool holder mounted on the housing, a percussion mechanism arranged within the housing which mechanism includes a ram reciprocating in a longitudinal direction and being adapted to apply impacts on a tool bit supported in the tool holder, a dampening mass which is slidably mounted in the longitudinal direction within the housing, wherein the dampening mass is biased towards a neutral position by a biasing element and wherein the dampening mass may be deflected from the neutral position against the biasing force of the biasing element. The dampening mass is formed of a ferromagnetic or paramagnetic material or comprises a permanent magnet and a solenoid is arranged within housing adjacent to the dampening mass such that the solenoid applies a force in the longitudinal direction on the dampening mass when being in the neutral position if a current is flowing through the solenoid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority, under 35 U.S.C. §119(a)-(d), to UK Patent Application No. GB 08 049 67.8 filed Mar. 18, 2008, the contents of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a powered hammer comprising a housing, a tool holder mounted on the housing, a percussion mechanism arranged within the housing which mechanism includes a ram reciprocating in a longitudinal direction and being adapted to apply impacts on a tool bit supported by the tool holder, a dampening mass which is mounted slidably in the longitudinal direction within the housing, wherein the dampening mass is biased towards a neutral position by a biasing element and wherein the dampening mass may be deflected from the neutral position against the biasing force of the biasing element.

BACKGROUND OF THE INVENTION

Such powered hammers can be employed to conduct demolition works wherein a tool bit formed as a chisel is usually driven into the material of the work piece. In addition, it can be conceived that the hammer is constructed as a hammer drill with a tool holder which is also rotationally driven. In this case a drill bit may be used as tool bit rather than a chisel.

In both cases considerable vibrations occur during use which are due to the percussion mechanism. These vibrations are transferred to the user via a handle mounted on the hammer housing and due to the high performance of chisel or demolition hammers the problem arises that the vibrations can reach a considerable strength and may cause damage to the user's health. Thus it is required to provide for an effective dampening mechanism.

From the prior art it is known to employ passive dampening systems in a powered hammer. For this purpose the handle can be decoupled from the main housing so as to reduce the amplitude of the vibrations transferred to the handle.

Furthermore, EP 1 252 976 A1 discloses a hammer with a dampening mass within the hammer housing which mass is movable in the moving direction of the ram and, thus, in the longitudinal direction wherein the mass is supported by two springs. The system comprising the mass and the springs is dimensioned in such a manner that the resonance frequency of the system corresponds to the frequency with which the ram impinges on the tool bit and the beat piece, respectively. During use the mass is stimulated to oscillate opposite to the reciprocating movement of the ram, and hence the overall vibrations of the hammer are reduced.

In addition, there are active dampening systems known from the prior art which systems employ a counter mass which is directly driven by the percussion mechanism wherein the counter mass is moving in an opposite direction relative to the ram.

However, the prior art dampening systems do not allow to control the amplitude and the time dependence of the movement of the dampening mass. In particular it is not possible to control the effect of the dampening system depending on the vibrations which are present on the housing of the hammer.

Moreover, the regulations regarding the maximum amplitude of vibrations occurring on hammers have recently been considerably tightened which results in a further need for a better vibration reduction on these tools.

Therefore, it is the object of the present invention to provide a powered hammer wherein the vibrations generated by a the hammer and transferred to a user are effectively reduced.

BRIEF SUMMARY OF THE INVENTION

According to the invention this object is achieved in that the dampening mass is formed of a ferromagnetic or paramagnetic material or comprises a permanent magnet and that a solenoid is arranged within housing adjacent to the dampening mass such that the solenoid applies a force in the longitudinal direction on the dampening mass when being in the neutral position if a current is flowing through the solenoid.

By means of the solenoid the dampening mass can be accelerated in a controlled manner due to the magnetic field generated by a current flowing through the solenoid. Thus, the arrangement of a solenoid and a magnetic dampening mass enables to selectively stimulate the dampening system.

In a preferred embodiment the hammer comprises a control unit which applies a current to the solenoid depending on a signal which is a measure for the acceleration of the housing in the longitudinal direction. This allows accelerating the dampening mass in response to the vibrations being present on the housing for reducing these vibrations. In particular, it is possible to mount an acceleration sensor on the tool housing.

However, it can be conceived that the solenoid is also effective as an acceleration sensor. In this case a low current is directed to the solenoid and variations of the resistance of the solenoid are detected which variations occur when the dampening mass enters the region of the solenoid. The time dependence of the variations allows determining the characteristics of the vibrations of the tool housing.

As an alternative, a second solenoid may be provided which is arranged such that the dampening mass when moving in the longitudinal direction approaches or departs from the second solenoid. In this case, the movement of the dampening mass and hence the vibrations of the hammer are determined based on the variation of the resistance of the second solenoid.

In any case, the signal generated by the acceleration sensor, the solenoid for accelerating the dampening mass or the second solenoid is used by the control unit to selectively direct a current through the solenoid in order to accelerate the dampening mass in an appropriate manner.

In a preferred embodiment, the percussion mechanism comprises a cylinder element in which the ram is movably located. The dampening mass has a circular shape and is arranged around the cylinder element wherein the dampening mass is supported by a spring extending in the longitudinal direction. Such an arrangement comprising the percussion and dampening mechanism has proven to be relatively space saving.

Here, it is preferred if the dampening mass is surrounded by a percussion mechanism housing wherein the solenoid is located along the circumference of the percussion mechanism housing spaced in the longitudinal direction from the neutral position of the dampening mass.

In case of a configuration with a percussion mechanism housing the solenoid may either be mounted on the outside of the housing with the solenoid being easily accessible or a ring shaped recess may be provided which is located in the surface of the percussion mechanism housing facing the dampening mass. In the latter case, the solenoid may be arranged close to the dampening mass which would require only small currents to accelerate the dampening mass. This would facilitate to employ the solenoid also as a sensor.

DETAILED DESCRIPTION OF THE INVENTION

A powered hammer according to a first embodiment of the present invention is shown inFIGS. 1 through 3. The hammer1comprises a housing3in which an electric motor (not shown in detail) is mounted. A handle5is provided at the rear end of the housing3which handle can be grasped by a user. In addition, the handle5comprises a trigger7to switch on the electric motor.

The electric motor is coupled with a percussion mechanism9which includes a cylinder element11in which a piston15is movably supported and reciprocatingly driven by a piston rod13coupled to a crank shaft. Furthermore, a ram17is arranged within the cylinder element11which is movable in a longitudinal direction that extends from the rear end of the cylinder element11to a tool bit19. Thus, the longitudinal direction coincides with the moving direction of the piston15and the ram17.

The ram17is adapted to apply impacts on the tool bit19supported in a tool holder20. However, the ram17does not directly hit the tool bit19but a beat piece21which is arranged between the ram17and the tool bit19. Depending on whether the tool holder20is also rotatingly driven, the tool bit19may be formed as a drill or a chisel bit.

The percussion mechanism is effective in a well known manner. Due to the air spring between the ram17and the piston15the ram17is reciprocating as a result of the reciprocating movement of the piston15. The ram17is hitting the beat piece21so that the kinetic energy as well as the momentum is transferred to the tool bit19. Thus, the percussion mechanism9applies impacts to the tool bit19.

The reciprocating movement of the ram17and the impacts of the ram17on the beat piece21and the tool bit19, respectively, result in vibrations which are sensed by a user. In order to reduce these vibrations a dampening mass23is provided which is mounted on the cylinder element11and is moveable in the longitudinal direction. The dampening mass23is supported between a front spring25and a rear spring27such that the dampening mass23is slideable in the longitudinal direction against the biasing force of the springs25,27.

The springs25,27have the effect that the dampening mass23is biased towards a neutral position shown in the drawings and defined by the dimensions of the springs from which position the dampening mass may be deflected.

The dampening mass23is formed from a material on which a magnetic field applies a force. Hence, it is possible that it is a paramagnetic material, a ferromagnetic material or it is a permanent magnet.

The percussion mechanism9is surrounded by a percussion mechanism housing29with a solenoid31mounted thereon wherein a ring shaped recess33is provided being located in the surface of the percussion mechanism housing29facing the dampening mass23. The solenoid31is positioned within the recess33along the circumference of the percussion mechanism housing29. In addition, the solenoid31and the recess33are arranged such that the solenoid31is spaced in the longitudinal direction from dampening mass23when being in the neutral position. This has the effect that a current flowing through the solenoid31results in force on the dampening mass23if it is in the neutral position.

Finally, an acceleration sensor35is mounted on the housing3which is connected with a control unit37. The unit37is in turn coupled to the solenoid31. As acceleration sensor37is possible to employ a piezo-resistive, a piezo-electrical or a capacitive sensor. These sensors are capable to convert an acceleration of the housing3into an electrical signal which is then sent to the control unit37. In response to the signal supplied by the sensor35the control unit37applies a current to the solenoid31to accelerate the dampening mass23in an appropriate manner by the resulting magnetic field. Accordingly, the solenoid31is supplied with a current in relation to a signal which is a measure for the acceleration of the housing3in the longitudinal direction.

With the assembly according to the present invention the movement of the dampening mass23may be controlled as follows. The time dependence of the acceleration of the housing3in the longitudinal direction will be detected by the acceleration sensor35and based on that measurand the solenoid31is supplied with a current to deflect the dampening mass23from the neutral position such that it moves in an opposite direction compared to the vibrations of the housing to reduce the amplitude of the vibrations or to cancel them out.

Whilst in this embodiment the vibrations are detected by an additional sensor35it may be conceived that in a first step the movement of the housing3as a result of the vibrations is detected by measuring the resistance of the solenoid31as a function of time. The resistance varies depending on the position of the dampening mass23with respect to the solenoid31, and thus allows determining the time dependence of the movement of the dampening mass23and the characteristics of the vibrations. The resistance may be measured by applying a small current to the solenoid31and calculating the corresponding resistance values based on the voltage drop. Based on the position of the dampening mass23determined via the resistance measurement, current pulses are applied to the solenoid31in order deflect the mass23in a controlled manner to reduce the vibrations.

FIG. 4shows an alternative configuration of the solenoid31with respect to the percussion mechanism housing29. Different to the embodiment shown inFIGS. 1 through 3, the solenoid31is located on the surface of the housing29facing away from the dampening mass.

Finally,FIGS. 5 and 6show an embodiment which employs a second solenoid39rather than an acceleration sensor. The second solenoid39is positioned adjacent to the first solenoid31within the ring-shaped recess33of the percussion mechanism housing.

Since the dampening mass23approaches or departs from the second solenoid39when moving in the longitudinal direction, the second solenoid39allows detecting the movement due to vibrations of the dampening mass23in the longitudinal direction as the resistance of the second solenoid39varies depending on the position of the dampening mass23. In order to detect this, a small current will be supplied to the second solenoid39and its resistance will be determined. The resistance will be employed as the signal based on which the solenoid31is supplied with a current to deflect the dampening mass23.

In conclusion, with the powered hammer according to the invention it is possible to reduce the vibrations generated by the percussion mechanism and transferred to a user wherein the dampening mass is accelerated by the solenoid31.