Tool driving or impacting – Impacting devices – Hammer head constitutes piston of drive motor
Reexamination Certificate
2000-02-11
2001-11-27
Smith, Scott A. (Department: 3721)
Tool driving or impacting
Impacting devices
Hammer head constitutes piston of drive motor
C173S208000, C173S212000, C173S171000, C173S204000
Reexamination Certificate
active
06321854
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a power tool comprising a body housing a member with a reciprocating percussive action (a percussion power tool), and also to a system for varying the deadweight of apparatus such as percussion power tools.
BACKGROUND ART
In the construction industry and other fields of heavy engineering such as mining, percussion power tools are widely used, for example to break up hard surfaces, compact loose material such as back-fill, and drive posts or piles into the ground. The tools incorporate a reciprocating mass, usually driven by compressed air but also by other means, which repeatedly impacts against a load-bearing surface within the tool. The movement of the mass towards the surface is known as the power stroke, whilst the reverse movement is known as the return stroke. It is known, for example in so-called hammer action drills, to incorporate a ratchet mechanism to rotate the tool during the return stroke.
The total work output of percussion power tools is dependent on the extent to which the reaction force between the tool and the work piece is able to counteract the force acting on the reciprocating mass during the power stroke. With hand-held systems acting on the ground, the reaction force is given by the sum of the deadweight of the tool and any downward pressure applied by the operator. The maximum deadweight for conventional heavy-duty paving breakers is approximately 40 kgs, otherwise the tool becomes too heavy to lift. The maximum deadweight for conventional heavy-duty rock drills is around 25 kgs; such drills tend to be held by the operator in a much higher position compared with paving breakers and therefore, for ergonomic reasons, they must be lighter.
There is a trend with hand-held percussion power tools to minimise the contribution of the operator to the reaction force in order to increase operator comfort and reduce the risk of contracting hand/arm vibration syndrome, HAVS.
DISCLOSURE OF THE INVENTION
In accordance with a first aspect of the present invention, there is provided a percussion power tool comprising a body housing a member with a reciprocating percussive action, a chamber coupled to the body, means for introducing fluid into the chamber, and means for subsequently emptying fluid from the chamber, fluid being stored in the chamber to increase the deadweight of the tool when the member is reciprocating or percussing, and subsequently emptied when it is idle.
The invention thus provides a variable deadweight, and hence variable inertia, percussion power tool. In practice, the deadweight may be selected such that, at its minimum, the tool is readily moved and, at its maximum, the required reaction force between tool and workpiece is achieved. In the case of hand-held percussion power tools, the contribution of the operator to the reaction force required for efficient use should be as low as possible at least when the deadweight is at its maximum. In this way, the magnitude of undesirable vibration and kickback transmitted to the operator is reduced.
The means for introducing fluid into the chamber may comprise a reservoir, supported independently of the body, for storing fluid for the chamber. The reservoir may comprise a pressurizable vessel. The means for emptying fluid from the chamber may communicate with the reservoir, enabling fluid from the chamber to be returned to the reservoir. Such a closed system enables fluid to be recycled. Since fluid is not required to flow to and from the chamber at the same time, a single fluid conduit may link the reservoir and chamber.
The chamber may comprise a membrane, perhaps forming a bladder, which flexes in sympathy with fluid filling or emptying from the chamber. The membrane may expand to line the inner periphery of the chamber as fluid fills the chamber. Alternatively, the membrane may expand to line the inner periphery of the chamber as fluid empties from the chamber. The membrane may assist the use of compressed gas to empty the chamber of fluid. Alternatively, the chamber may house a sliding partition element (e.g. a piston) which moves in sympathy with fluid being introduced into or emptied from the chamber.
The reservoir may similarly comprise a membrane or piston which respectively flexes or slides in sympathy with fluid filling or emptying from the reservoir.
In one embodiment, the means for introducing fluid into the chamber and/or the means for emptying fluid from the chamber may be operated by compressed gas. The means for introducing fluid into the chamber and/or means for emptying fluid from the chamber and reciprocation of the member may be operated by compressed gas from a common supply. Compressed gas may be used to displace fluid in the chamber in order to drain the fluid from the chamber. Compressed gas may also be used to displace fluid in the reservoir in order to fill the chamber with displaced fluid. The percussion power tool may further comprise valve means for coupling to a compressed gas supply, the valve means controlling fluid displacement for filling and emptying the chamber and the reciprocating percussive action of the member in the tool (pneumatic action).
The valve means may comprise an arrangement combining compressed gas supply valves alternately for supplying compressed gas to the chamber and the reservoir, and bleed valves for alternately releasing compressed gas from the chamber and the reservoir in such a way that compressed gas supply to only one of the chamber or the reservoir activates release of compressed gas from the other only. The arrangement may thus be fed from a single line of compressed gas. Alternatively, the chamber and the reservoir may be fed from different lines of compressed gas, possibly from different compressors, thereby obviating the need for a conduit conveying compressed gas between the chamber and the reservoir. Synchronisation of the compressed gas supply and bleed valves of the chamber and reservoir may be achieved in various ways. For example, electrical interconnection of the valve actuators could be used to ensure that the opening of the supply valve of one of the chamber and reservoir is accompanied by the opening of the bleed valve of the other, all remaining valves being closed. Alternatively, a signal from pressure sensing means provided with the compressor for controlling compressor output could be used to operate the valves at the reservoir end.
The percussion power tool may further comprise drive means for reciprocating the member in the body, the drive means being arranged to drive a gas compressor which provides compressed gas for introducing fluid into and/or emptying fluid from the chamber. The gas compressor may be in the body. Compressed gas may be generated by compression of gas ahead of or adjacent the member when reciprocating. The drive means may comprise a linear motor, and the linear motor may comprise a free piston device.
In another embodiment, the percussion power tool may have hydraulic drive means for reciprocating the member in the body. The hydraulic fluid for the hydraulic drive means may also be supplied to the chamber for increasing the deadweight of the tool. There may be provided means for converting high pressure, low flow rate (e.g. 80 bar, less than 50 litres/min) hydraulic fluid for the hydraulic drive means into low pressure, high flow rate hydraulic fluid for the chamber. The converting means may comprise an ejector pump.
In general terms, the percussion power tool may have at least two chambers coupled to the body, each for receiving fluid to increase the deadweight of the tool. The at least two chambers may be symmetrically disposed around the body. Preferably, there are means for providing even distribution of fluid between the at least two chambers, thus giving a balanced weighting to the percussion power tool. For example, equal fluid flow split between two or more chambers may be achieved by equalling the head losses through different flow paths in a distribution manifold. Fine adjustment of the headlosses may be achieved by chamfering different
Smith Scott A.
Townsend and Townsend / and Crew LLP
LandOfFree
Power tool does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Power tool, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power tool will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2582800