EP1008422A2 - Method and device for handheld machine tools to prevent accidents caused by tool blockage - Google Patents

Abstract

The method and the device for avoiding accidents due to tool blocking when working with a hand-held machine tool (M) with a rotating tool (8), e.g. rotary hammer, with an interrupter device (5, 6) for interrupting the action of the drive motor (7) on the Tool (8) depending on the operating state detected by a motion measuring device (1) is characterized according to the invention in that the motion measuring device preferably has two acceleration sensors (1a, 1b), whose measured values (a ₁ , a ₂ ) before another Signal evaluation can be subtracted. As a result, blockage accidents with an oblique or distorted tool axis can be reliably detected and, moreover, the acceleration due to gravity is compensated as a disturbance variable for every possible application position of the machine tool. When evaluating the acceleration signal in the event of tool blocking, measurement signals describing the current machine condition are used.

Description

The invention relates to a method and to the application of the Procedure based facility to prevent accidents by Tool blocking when working with hand-held machine tools rotating tool, especially with rotary hammers, with an interrupter device to interrupt the effect of the drive motor on the Tool depending on that supplied by a motion measuring device Rotational movement size detected operating state is equipped.

Rotational accidents, in particular injuries to the wrist or arms or the fall of ladders, scaffolding, etc. due to the sudden blockage of the tool and the associated rapid Increase in reaction torque for hand-held machine tools, especially those of higher performance, such as hammer drills, are long recognized and much discussed problem. From the multitude of known ones Approaches to solving this problem are only exemplary of the publications EP 150 669 A2 and WO 88/06508 A3. By using it one arranged inside or on the housing of the machine tool Twist sensor, in particular an acceleration sensor that the Acceleration of an external swiveling movement of the hand-held machine tool is recorded - possibly depending on various default criteria, e.g. an acceleration threshold - a clutch triggers the drivetrain between the drive motor and the actual tool unit, in particular the drilling spindle, interrupts. Difficulties with the two known, similar approaches arise from the fact that it is also in a desired operational use of the Machine, for example when working with a hammer drill in a concrete mass inhomogeneous composition for false tripping of the safety clutch is coming. This depends on the basic approach of an immediate Signal evaluation without a subsequent assessment together, i.e. a signal evaluation with necessarily a comparatively low security threshold without individual assessment of the respective accident.

A major improvement was made with a predictive assessment process for the signals delivered by an acceleration sensor, as described in the patent DE 43 44 817 C2. This improved The process is based on the idea of specifying a time constant based on the amount of rotary motion supplied by the acceleration sensor of the reaction torque when blocking or partially blocking the Predicting the tool's expected torsion angle to calculate and then activate the safety clutch when the calculated twist angle to be expected a specifiable maximum permissible Angle of rotation would exceed. The future behavior of the Machine evaluated immediately after an accident and a countermeasure triggered when the machine tool with an angular momentum has been acted on, by which an accident can no longer be avoided.

(1) die Rotationsachse des Werkzeugs liegt häufig im entscheidenden Augenblick des Blockierens nicht zwangsläufig in der Werkzeugachse; und

(2) die Erdbeschleunigung beeinflußt das Meßsignal des Beschleunigungsmessers, und zwar abhängig von der momentanen Lage des Werkzeugs.

However, the promising approach for the practice of such hand-held machine tools according to the mentioned DE publication still has two main problems, which have been found in test series:

(1) the axis of rotation of the tool often does not necessarily lie in the tool axis at the decisive moment of blocking; and

(2) Gravitational acceleration affects the accelerometer measurement signal depending on the current position of the tool.

The invention is therefore based on the object, hand-held machine tools to improve the type mentioned so that a Blocking of the tool by the reaction impulse or the reaction moment A measurement signal triggered by the motion sensor is then also an unambiguous one Provides information about a dangerous blocking case if the axis of rotation of the tool is distorted in the event of a malfunction, with the influencing variable simultaneously Acceleration to gravity on the measurement signal should be switched off.

The invention is in a method for preventing accidents Tool blocking when working with hand-held machine tools rotating tool, especially with rotary hammers, with an interrupter device to interrupt the effect of the drive motor on the Tool depending on that by a motion measuring device supplied inventory is equipped, characterized in that the movement of the machine tool at least two spatially apart and against the axis of rotation in normal operation of the Tool spaced points of the machine tool is measured, and that the measured values obtained before further processing and evaluation be subtracted from each other.

A facility to prevent rotational accidents due to Tool blocking in a hand-held machine tool with rotating Tool according to the type described above is characterized in that at least two acceleration sensors, preferably - in particular from Cost reasons - linear acceleration sensors as torsion sensors within of the housing of the machine tool on spatially from each other and opposite the tool axis preferably differently spaced locations are mounted and that the electronic evaluation unit has a subtraction level contains in which the signals delivered by the acceleration sensors before calculating one intended to trigger the interrupter device Signal are subtracted from each other.

Advantageous additions and designs for the inventive Procedures and the facility based on them are the content of each dependent claims.

Preferably and in particular the method according to the invention and the safety device based thereon an improvement in the mentioned DE document described solution, the one of the several Acceleration sensors each delivered signals before calculating the expected and predeterminable angle of rotation of the machine tool from each other be subtracted.

With regard to the calculation of the expected twist angle, the reduction or elimination of low or high frequency interference as well as the appropriate mathematical principles and algorithms for reliable predictive Calculation of the critical twist angle to be expected again refer to DE 43 44 817 C2.

Fig. 1A bzw. 1B

die schematische Darstellung eines Bohrhammers in Seiten- bzw. Rückansicht als Beispiel für eine handgeführte Werkzeugmaschine, die mit zwei Beschleunigungssensoren ausgerüstet ist;

Fig. 2

die schematische Teilschnittdarstellung des Bohrhammers nach Fig. 1; und

Fig. 3

die Prinzipdarstellung eines Drehbewegungsmodells für eine Handwerkzeugmaschine gemäß Fig. 1, die im dargestellten Beispiel mit zwei Linear-Beschleunigungssensoren ausgerüstet ist.

The invention and advantageous details are explained in more detail below with reference to the drawing in an exemplary embodiment. Show it:

1A and 1B

the schematic representation of a rotary hammer in side or rear view as an example of a hand-held machine tool which is equipped with two acceleration sensors;

Fig. 2

the schematic partial sectional view of the hammer drill according to Fig. 1; and

Fig. 3

the basic representation of a rotary motion model for a hand tool according to FIG. 1, which is equipped in the example shown with two linear acceleration sensors.

1A / B and FIG. 2 show the essentials in a basic illustration Components of a hand-guided in the context of the invention Machine tool M, its operating state by means of two acceleration sensors 1a or lb is monitored. In Fig. 1B is indicated by arrows indicated which acceleration 10 or deflection force in which deflection direction 11 on the machine tool in case of blocking of the tool 8 act. Via an input interface 2 for signal shaping, A / D conversion, etc., the signals from the acceleration sensors 1a, 1b arrive an electronic evaluation unit 3, which is a microprocessor, one in discrete Circuit technology implemented microcomputer, a signal processor or the like can be. The digitized signals are in this evaluation unit 3 of the acceleration sensors 1a, 1b are first subtracted from one another, such as explained and justified further below. Then the so obtained Result evaluated using a model or rule-based algorithm, which the operating state of the hand machine tool M when the Acceleration sensors 1a, 1b predicts. However, the invention can be also be used advantageously for those applications in which there are no predictive ones Calculation of the expected twist angle of the hand machine tool M takes place, that is to say in the case of those safety devices that do so Assess acceleration signal generated by tool blocking immediately and when a certain level is exceeded, possibly after interference signal filtering, as well as one and / or two integration, directly to trigger the Use drive interrupter device.

If an acceleration is detected by tool blocking, which is caused by the Evaluation unit 3 is classified as "dangerous", so is via an output interface 4 the operating interruption device, in particular one Clutch 5 actuates the drive train between a drive motor 7 and the tool holder or tool 8 interrupts and if necessary additionally triggers a circuit breaker 6.

The method according to the invention and the measuring system based thereon have an effect reliable for any rotation axis of the overall system as well as for if necessary, tilted or warped tool axis, as below under 3 is explained.

As already mentioned, the movement measuring device has at least two Acceleration sensors 1a, 1b, whose measurement results according to the invention subtracted from further processing. As can be seen from the following Derivation for two possible applications can be seen, the disturbance Gravitational acceleration for every possible application position of the power tool eliminated.

3 it is provided that the second sensor 1b in a axis 9 including the axis of rotation in normal operation Level lies. However, the axis of rotation can be assumed to be two-dimensional Take any position and always delivers error-corrected signal, as derived from the following mathematical derivation reveals. In principle, more than two sensors can also be provided be, then by averaging or a plausibility check the reliability of the signal obtained is increased. If two redundant sensor pairs are provided, the intervals for one Security check to be stretched in principle.

a₁, a₂ =

Meßsignale des ersten Beschleunigungssensor 1a bzw. des zweiten Beschleunigungssensors 1b; insbesondere repräsentieren a₁ und a₂ lineare Tangentialbeschleunigungen um jeweilige Drehachsen, die nachfolgend als "Fall 1" bzw. als "Fall 2" einer näheren Betrachtung unterzogen werden.

d =

Abstand der Beschleunigungssensoren 1a, 1b;

r_1a1, r_1b1 =

Abstände der Beschleunigungssensoren 1a, 1b für den "Fall 1", bei dem die (gedachte) Drehachse des Werkzeugs, beispielsweise im Fall des Werkzeugblockierens gegenüber der Antriebsachse bzw. Drehachse im Normalbetrieb nach unten versetzt ist; und

r_1a2, r_1b2 =

Abstände der Beschleunigungssensoren 1a, 1b von einer (gedachten) Drehachse für den "Fall 2", d.h., wenn die Drehachse des Werkzeugs im Falle des Blockierens gegenüber der Antriebsachse bzw. Drehachse im Normalbetrieb nach oben versetzt ist;

ϕ =

zu erwartender Drehwinkel im Falle des Werkzeugblockierens.

The quantities indicated in FIG. 3 denote the following:

a ₁ , a ₂ =

Measuring signals of the first acceleration sensor 1a and the second acceleration sensor 1b; in particular, a ₁ and a _{2 represent} linear tangential accelerations about respective axes of rotation, which are subsequently examined in more detail as "case 1" and "case 2".

d =

Distance of the acceleration sensors 1a, 1b;

r _1a1 , r _1b1 =

Distances of the acceleration sensors 1a, 1b for "case 1", in which the (imaginary) axis of rotation of the tool, for example in the case of tool blocking, is offset downward from the drive axis or axis of rotation in normal operation; and

r _1a2 , r _1b2 =

Distances of the acceleration sensors 1a, 1b from an (imaginary) axis of rotation for "case 2", that is to say when the axis of rotation of the tool is offset upwards in the event of blocking relative to the drive axis or axis of rotation in normal operation;

ϕ =

expected angle of rotation in the event of tool blocking.

d = r1a1 + r1b1 a1r1b1 = - a2r1a1 a1r1b1 + a1r1a1 = - a2r1a1 + a1r1a1 a1(r1a1 + r1b1) = r1a1(a1 - a2) a1 r1a1 = a1 - a2 r1a1+r1b1 Mathematical derivation for "Case 1":

d = r 1a1 + r 1b1 a 1 r 1b1 = - a 2nd r 1a1 a 1 r 1b1 + a 1 r 1a1 = - a 2nd r 1a1 + a 1 r 1a1 a 1 (r 1a1 + r 1b1 ) = r 1a1 (a 1 - a 2nd ) a 1 r 1a1 = a 1 - a 2nd r 1a1 + r 1b1

Equation (3) used in equation (1) in conjunction with equation (2) yields:

nicht mehr abhängig von der Erdbeschleunigung, da der Anteil der Erdbeschleunigung in beiden Beschleunigungssensorsignalen a₁ bzw. a₂ in gleicher Größe vorhanden ist, wie sich aus Gleichung (4) ersehen läßt, also vollständig kompensiert wird. Obviously the value

no longer depends on the acceleration due to gravity, since the proportion of the acceleration due to gravity is present in the same magnitude in both acceleration sensor signals a ₁ and a ₂ , as can be seen from equation (4), that is to say is completely compensated for.

d = r1a2 - r1b2 -a1r1b2 = - a2r1a2 -a1r1b2 + a1r1a2 = - a2r1a2 + a1r1a2 a1(r1a2 - r1b2) = r1a2(a1 - a2) a1 r1a2 = a1 - a2 r1a2 - r1b2 Mathematical derivation for "Case 2":

d = r 1a2 - r 1b2 -a 1 r 1b2 = - a 2nd r 1a2 -a 1 r 1b2 + a 1 r 1a2 = - a 2nd r 1a2 + a 1 r 1a2 a 1 (r 1a2 - r 1b2 ) = r 1a2 (a 1 - a 2nd ) a 1 r 1a2 = a 1 - a 2nd r 1a2 - r 1b2

Equation (3 ') inserted in equation (1') in conjunction with equation (2 ') gives:

So also for "Case 2" applies that is available for signal evaluation standing value of the measurement signal, i.e. the rotational acceleration, is no longer dependent is of the same mass attraction for both acceleration sensors or gravitational acceleration.

In principle, any measuring system is suitable within the scope of the invention Acceleration sensors or accelerometers, i.e. those that are based on piezoelectric, piezoresistive or inertial and / or integrated as Part of a microelectronic circuit are realized. The electronic Evaluation unit can either be implemented analogously with the help of Operational amplifiers and corresponding filter circuits or digital using a microprocessor with associated processor interfaces (see DE 43 44 817 C2). It is also possible to use the evaluation unit to realize as fuzzy logic, which is detailed in DE 196 41 618 A1 is described.

In order to implement the principle on which the invention is based, it is in principle any known measurement method for acceleration, angular velocity or Angle of rotation applicable. In the above embodiment, is mainly from Cost reasons based on linear acceleration sensors, for example referred to piezoelectric measurement methods. In principle, are suitable however also pulse wheel and magnetic angle stepper, micromechanical Accelerometers, optical measurement methods, magnetohydrodynamic Measuring method, rotational acceleration measuring method according to the Ferraris principle, capacitive measuring methods or strain gauge accelerometers.

Claims (7)

Method for avoiding accidents caused by tool blocking when working with a hand-held machine tool with a rotating tool (8), in particular for rotary hammers, which have an interrupter device (5, 6) for interrupting the action of the drive motor (7) on the tool (8) as a function of it is equipped with the operating state detected by a motion measuring device (1), characterized in that the movement of the machine tool in space is measured at at least two points on the machine tool spaced apart from one another and against the tool axis, and in that the measured values obtained (a ₁ , a ₂ ) are subtracted from each other before the calculation of a signal triggering the interrupter device (5, 6). Method according to Claim 1, characterized in that the movement of the machine tool in space is measured at points which are at different distances from the tool axis. Method according to Claim 1 or 2, characterized in that the acceleration of the machine tool in space at at least two locations spaced apart from one another is recorded as the movement variable. Method according to Claim 3, characterized in that after the subtraction of the measured values supplied by at least two acceleration sensors, specifying a time constant from the rotational acceleration quantity obtained by the subtraction, an anticipated angle of rotation (ϕ) of the machine tool (M) is calculated in advance and the interrupter device (5, 6) is activated as soon as the calculated, expected twist angle exceeds a predeterminable maximum permissible twist angle. Device for avoiding accidents due to tool blocking in a hand-held machine tool with a rotating tool, in particular rotary hammers, which has an interrupter device (5, 6) for interrupting the action of the drive motor (7) on the tool (8) as a function of that by means of an acceleration measuring device (1) detected operating state, characterized in that the acceleration measuring device is equipped at least two acceleration sensors (1a, 1b) mounted within the housing of the machine tool at locations spaced apart from one another and with respect to the tool axis, and that the acceleration signals (a ₁ , a ₂ ) the electronic evaluation unit (3) processing the acceleration sensors contains a subtraction stage in which the signals supplied by the acceleration sensors each subtly before the calculation of a trigger signal for the interrupter device (5, 6) be shaved. Device according to claim 5, characterized in that the acceleration sensors (1a, 1b) are linear acceleration sensors. Device according to claim 5, characterized in that at least one of the acceleration sensors (1a, 1b) is arranged in such a way that it delivers a maximum output signal in the normal operating position of the machine tool.

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