# US 8,087,472 B2 · Vibration dampening system for a power tool and in particular for a powered hammer > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,087,472 B2 - Document ID: US8087472B2 - Status: Granted - Kind: B2 - Application number: 12/533,280 - Filed: 2009-07-31 - Published: 2011-02-03 - Granted: 2012-01-03 - Earliest claimed: 2009-07-31 - Assignees: Black & Decker Inc. - Inventors: Robert Alan Usselman; Benjamin Schmidt - Web page: https://patentgrep.com/patent/US8087472B2 ## CPC - B25D 17/24: Damping the reaction force {(resiliently mounted handles B25D17/043; dampers in connections of hammers to backhoes E02F3/966)} - B25D 2217/008: being electronically-driven - B25D 2217/0092: being spring-mounted - B25D 2250/221: Sensors - B25D: PERCUSSIVE TOOLS {(percussive machines for forging B21J; hand-held drilling machines, in general B23B45/00, for wood B27C3/08; drilling machines, used for mining or quarrying, with reciprocating tool which is turned intermittently when out of contact with the working face E21B1/00)} ## Abstract The present invention relates to a method for controlling a power tool comprising a housing, an electric motor, a tool holder for supporting a tool bit and a conversion mechanism for converting the rotational movement of the output shaft of the motor into a reciprocating movement of the tool bit when being supporting in the tool holder, wherein oscillations of an element of the power tool are detected, wherein a quantity characterizing the oscillations is monitored and wherein the rotational speed of the electric motor is controlled such that the quantity does not exceed a preset value. ## Claims ### Claim 1 A method of controlling a power tool comprising: a housing, an electric motor, a tool holder for supporting a tool bit and a conversion mechanism for converting the rotational movement of the output shaft of the motor into a reciprocating movement of the tool bit when being supporting in the tool holder, wherein oscillations of an element of the power tool are detected, wherein a quantity characterizing the oscillations is monitored and wherein the rotational speed of the electric motor is controlled such that the quantity does not exceed a preset value. ### Claim 2 (depends on 1) The method according to claim 1, wherein the power tool is a powered hammer comprising a hammer mechanism including a ram which reciprocates along a moving axis and applies impacts on the tool bit when being supported in the tool holder, the hammer mechanism being operatively coupled to the electric motor via the conversion mechanism. ### Claim 3 (depends on 2) The method according to claim 2, further providing a counter mass movably supported in the housing, the counter mass being biased towards a neutral position by at least one spring element and being capable of oscillating around the neutral position in a direction which is parallel to the moving axis of the ram, and wherein a quantity of motion of the oscillations with which the counter mass oscillates is determined when the electric motor is activated, and wherein the rotational speed of the electric motor is controlled such that the quantity of motion assumes a preset value. ### Claim 4 (depends on 3) The method according to claim 3, wherein an amplitude of the oscillations with which the counter mass oscillates, is determined when the electric motor is activated and wherein the rotational speed of the electric motor is controlled such that the oscillation amplitude assumes a preset value. ### Claim 5 (depends on 3) The method according to claim 3, wherein the hammer further comprises a coil surrounding the path along which the counter mass oscillates, wherein the counter mass is formed of a metal, and wherein the inductance of the coil is monitored as a function of time for determining the quantity of motion. ### Claim 6 (depends on 5) The method according to claim 5, wherein the hammer comprises first and second coils being symmetrically arranged with respect to the neutral position of the counter mass and wherein the quantity of motion is determined via simultaneously monitoring the inductance of the first and second coils. ### Claim 7 (depends on 5) The method according to claim 5, wherein the quantity of motion being determined is the amplitude of the oscillations with which the counter mass oscillates. ### Claim 8 (depends on 3) The method according to claim 3, wherein the hammer further comprises a Hall sensor being positioned adjacent to the neutral position of the counter mass, wherein the counter mass comprises a magnet element and wherein the quantity of motion is determined via detecting the duration of the time interval in which the magnet affects the Hall sensor. ### Claim 9 (depends on 3) The method according to claim 3, wherein the hammer further comprises a plurality of Hall sensors being arranged adjacent to the path along which the counter mass oscillates, the distance the Hall sensors have to the neutral position differing for each Hail sensor, wherein the counter mass comprises a magnet element and wherein the quantity of motion is determined via monitoring which Hall sensors are affected by the magnet located on the counter mass. ### Claim 10 A Power tool comprising: a housing, an electric motor, a tool holder for supporting a tool bit and a conversion mechanism for converting the rotational movement of the output shaft of the motor into a reciprocating movement of the tool bit when being supporting in the tool holder, a detection device for detecting oscillations of an element of the tool wherein the device outputs a signal characterizing the oscillations, and a control unit coupled with the electric motor and the detection device, the unit being adapted such that the rotational speed of the electric motor is controlled so that a quantity characterizing the oscillations and determined based on the signal does not exceed a preset value. ### Claim 11 (depends on 10) The power tool according to claim 10, wherein the too; is a hammer comprising a hammer mechanism including a ram which is reciprocatingly driven along a moving axis to apply impacts on the tool bit when being supported in the tool holder, the hammer mechanism being coupled to the electric motor via the conversion mechanism. ### Claim 12 (depends on 11) The power tool according to claim 11 further comprising a counter mass movably supported in the housing, the counter mass being biased towards a neutral position by at least one spring element and being capable of oscillating around the neutral position in a direction which is parallel to the moving axis of the ram, wherein the control unit is adapted to determine a quantity of motion of the oscillations with which the counter mass oscillates, when the electric motor is activated, and wherein the control unit is adapted such that the rotational speed of the electric motor is controlled so that the quantity of motion does not exceed a preset value. ### Claim 13 (depends on 12) The power tool according to claim 12, wherein the control unit is adapted to determine the amplitude of the oscillations with which the counter mass oscillates, when the electric motor is activated, and wherein the control unit is adapted such that the rotational speed of the electric motor is controlled so that the oscillation amplitude assumes a preset value. ### Claim 14 (depends on 12) The power tool according to claim 12, wherein the detection device comprises a coil surrounding the path along which the counter mass oscillates and wherein the counter mass is formed of a metal. ### Claim 15 (depends on 14) The power tool according to claim 14 wherein the detection device comprises first and second coils being symmetrically arranged with respect to the neutral position of the counter mass. ### Claim 16 (depends on 12) The power tool according to claim 12, wherein the detection device comprises a Hall sensor being arranged adjacent to the neutral position of the counter mass and wherein the counter mass comprises a magnet element. ### Claim 17 (depends on 12) The power tool according to claim 12, wherein the detection device comprises a plurality of Hail sensors being arranged adjacent to the path along which the counter mass reciprocates wherein the counter mass comprises a magnet element and wherein the distance the sensors have to the neutral position differs for each sensor.