EP1201373B1 - Safety circuit for a rotary electric hand tool - Google Patents

Description

The invention refers to a safety circuit for an at least partially rotating electric hand tool device such as a drill or a hammer drill.

To avoid impermissible twisting of the handle of the housing, for example caused by tool blocks, the power flow from the electric drive to the work spindle is interrupted by safety clutches.

After DE4334933A1 In a rotary electric hand tool device, the vibration is measured transversely to the axis of rotation via an acceleration sensor and viewed over time in a predefined time interval. If a zero crossing does not occur within this time interval, which is necessary and thus characteristic for a stable angular position relative to the axis of rotation, the power flow from the electric drive to the work spindle is interrupted by a sensor. Within the time interval, high rotational accelerations can not be detected.

After DE3707052 For example, in order to prevent inadvertent rotations of the handle of a rotary hammer during tool blockage, generally either a rotational angle, a rotational speed or a rotational acceleration sensor is used. To interrupt the power flow of the current state is evaluated.

After DE4334933A1 the rotation acceleration is measured with a rotational acceleration sensor and the predicted future deflection angle of the housing is calculated for a predefined future time interval after an analog or digital realized frequency band-limited integration, which leads to interruption of the force flow after exceeding a limit value.

Furthermore, after the US5247252 Generally, a Coriolis force-sensing piezoceramic yaw rate sensor is used to determine rotational speed.

The object of the invention is to reduce the components required for the realization of a safety circuit based on the future deflection angle for the interruption of the force flow of a rotating electric hand tool device during tool blocks.

The object is essentially achieved by the features of the independent claims. Advantageous developments emerge from the subclaims.

Essentially, for generating the control signal for interrupting the power flow and / or the current path of a rotating electric hand tool, a rotational speed directly measuring rotational rate sensor and connected to the sensor output, the rotational speed at least partially proportional measurement value to a threshold comparative comparative member connected to each other.

The approximation of a constant rotational acceleration permissible with 1 ms to 100 ms (advantageously approx. 20 ms) for the rotating electrical hand tool units due to the inertia of the rotating components of the drive train, is calculated to be zero at the beginning of the time interval for the sake of simplicity set, rotation angle according to the linear equation of motion for uniform rotational movements approximately proportional to the directly measured rotational speed, whereby a, containing an integration of a rotational acceleration term in the functional unit does not need to be realized.

The rotation rate sensor is advantageously designed as an active, fully integrated, piezoceramic or silicon-based sensor which operates on the basis of the Coriolis force, which requires little space and only an external circuit limited to the power supply.

Advantageously, the measured value is filtered via an intermediate low-pass filter with a cut-off frequency between 10 Hz and 100 Hz for suppressing high-frequency acceleration peaks, which occur in particular during impact-assisted machining of rock. An analog low-pass filter is further advantageously realized via an RC combination.

Further advantageously, the measured value via an intermediate high-pass filter, which can be performed in conjunction with a subsequent resistor as a suitably dimensioned capacitor, with a cutoff frequency between 0.5 Hz and 10 Hz to suppress the gewillgurten guiding movement of the user filtered, which must not trigger an interruption of the power flow.

It is advantageous between the rotation rate sensor and the comparison member, a weighted summing, which, for example, consists of a resistance voltage divider, arranged with an upstream integrating, which, for example, consists of an above the cutoff frequency operated RC low pass. By now the weighted summing proportional to the rotation angle and proportional to the rotational speed present two time functions, the general solution for predicting the future rotation angle is approximately electronically realized even at non-zero boundary conditions, whereby the user within a permanently monitored limits a rotation angle interval is granted, the starting point advantageous is determined at the switch-on of the electric drive.

Alternatively, the digitized via an A / D converter measured value of the rotation rate sensor in a, preferably time-periodically interruptive or switched on microcontroller with standard software algorithms are evaluated, advantageously the summing as a numerical addition, the integrator as an incrementally extended sum and the Filter over weighted, incrementally sliding filled partial sums are realized.

Advantageously, the control signal derived after comparison with a predetermined threshold value interrupts the current path of the electric drive and / or a controllable coupling unit via a controllable circuit breaker from the electric drive to the tool spindle.

• Fig. 1 als drehendes Elektrohandwerkzeuggerät mit Sicherheitsschaltung
• Fig. 2 als analoge Sicherheitsschaltung
• Fig. 3 als digitale Sicherheitsschaltung

The invention will be explained in more detail with respect to an advantageous embodiment with:

• Fig. 1 as a rotating electric hand tool with safety circuit
• Fig. 2 as analogue safety circuit
• Fig. 3 as a digital security circuit

To Fig. 1 has an electric hand tool 1 rotating about a rotation axis A for interrupting the power flow from an electric drive 2 to a rotating tool spindle 3 via a control signal θ controllable coupling means 4, a controllable via the control signal θ power switch 5 in the current path of the electric drive 2 and an analog safety circuit 6 with one, the rotational speed ω directly measuring yaw rate sensor 7 on.

To Fig. 2 In the case of an analogue safety circuit 6, the output of the rotational rate sensor 7 measuring the rotational speed .omega. is signal-transmitting connected to a comparison element 8 which is designed as a comparator and compares the measured value M, which is at least partially proportional to the rotational speed .omega., to a preselectable threshold value S. Between the yaw rate sensor 7 and the comparator 8 which is triggered by the switch-on time of the electric drive, an analogous functional unit 9 having a timed transfer function is arranged.

mit s = σ + jω (komplexe Kreisfrequenz)
und der oberen Grenzfrequenz ${\mathit{f}}_{\mathit{g}}=\frac{1}{2\mathit{\pi }{R}_1{C}_1}$

von auf 10Hz.The components R1 and C1 form a low-pass filter with the transfer function: $A_{\mathit{TP}}\left(s\right)=\frac{1}{1+s{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="imgf0002.png"\; state="\{\{state\}\}">R</figure-callout>}}_1{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="imgf0002.png"\; state="\{\{state\}\}">C</figure-callout>}}_1}$

with s = σ + j ω (complex angular frequency)
and the upper limit frequency ${\mathit{f}}_{\mathit{G}}=\frac{1}{2\mathit{\pi }{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="imgf0002.png"\; state="\{\{state\}\}">R</figure-callout>}}_1{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="imgf0002.png"\; state="\{\{state\}\}">C</figure-callout>}}_1}$

from to 10Hz.

und der unteren Grenzfrequenz ${\mathit{f}}_{\mathit{g}}=\frac{1}{2\mathit{\pi }{R}_2{C}_2}$

von 0.5Hz.The components C2 and R2 form a high-pass filter with the transfer function: $A_{\mathit{HP}}\left(s\right)=\frac{1}{1+\frac{1}{s{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="imgf0002.png"\; state="\{\{state\}\}">R</figure-callout>}}_2{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="imgf0002.png"\; state="\{\{state\}\}">C</figure-callout>}}_2}}$

and the lower limit frequency ${\mathit{f}}_{\mathit{G}}=\frac{1}{2\mathit{\pi }{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="imgf0002.png"\; state="\{\{state\}\}">R</figure-callout>}}_2{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="imgf0002.png"\; state="\{\{state\}\}">C</figure-callout>}}_2}$

from 0.5Hz.

The components R3 and C3 form an integrator, which is realized as above its cutoff frequency of 0.01 Hz operated low pass. The resistors R4, R5 and R6 form an adder in their combination, with the proviso R ₄ = R ₅ = R. ₆ In the comparison element 8, the resulting measurement signal M 'is compared with a threshold value S as the switch-off condition. This leads, if necessary, to the separation of the drive train.

, beim Tiefpassfilter II nach ${\mathit{A}}_{\mathit{Int}}\left(\mathit{s}\right)=\frac{1}{s+{\omega }_{\mathit{Int}}}$

und beim Integrator III nach $A_{\mathit{TP}}\left(s\right)=\frac{{\omega }_{\mathit{TP}}}{s+{\omega }_{\mathit{TP}}}$

wobei sich die Grenzfrequenzen jeweils aus ${\mathit{f}}_{\mathit{g}}=\frac{1}{2\pi }\mathrm{\omega }$

ω berechnen. Für das gewichtete Summierglied IV beträgt Tau ungefähr 0.02.To Fig. 3 includes as a software program of between a analog-to-digital converter (ADC) and a digital-to-analog converter (DAC) arranged microcontroller digitally triggered with the switch-on of the electric drive triggered, functional unit 9 'as functional sub-blocks a digital high-pass filter I, in which previously normalized the input signal via a multiplier with 1 / E, a digital low-pass filter II, an integrator III and a weighted summation element IV for weighting the rotational speed ω with the factor Tau. The transfer functions of the functional sub-blocks are calculated using the high-pass filter I ${\mathit{A}}_{\mathit{HP}}\left(\mathit{s}\right)=\frac{s}{s+{\omega }_{\mathit{HP}}}$

, after the low-pass filter II ${\mathit{A}}_{\mathit{Int}}\left(\mathit{s}\right)=\frac{1}{s+{\omega }_{\mathit{Int}}}$

and at the Integrator III $A_{\mathit{TP}}\left(s\right)=\frac{{\omega }_{\mathit{TP}}}{s+{\omega }_{\mathit{TP}}}$

where are the cutoff frequencies each out ${\mathit{f}}_{\mathit{G}}=\frac{1}{2\pi }\mathrm{\omega }$

calculate ω. For the weighted summer IV, tau is about 0.02.

Claims (10)

1. Safety circuit for generating a control signal (Θ) when the future angle of deflection of the casing of an at least partly rotary electric hand tool (1) is exceeded, characterized in that a rate of rotation sensor (7) directly measuring the rotational speed (ω) is connected for signal transmission purposes to a comparing element (8).
2. Safety circuit according to Claim 1, characterized in that the rate of rotation sensor (7) is realized as an active sensor measuring on the basis of the Coriolis force.
3. Safety circuit according to Claim 1 or Claim 2, characterized in that a functional unit (9, 9') is arranged for signal transmission purposes between the rate of rotation sensor (7) and the comparing element (8).
4. Safety circuit according to any one of the preceding claims, characterized in that the functional unit (9) comprises a weighted summing element (IV) with an integrating element (III) connected to its input.
5. Safety circuit according to any one of Claims 1 to 3, characterized in that the functional unit (9) is realized without means for integrating the rotational acceleration (ω).
6. Safety circuit according to any one of the preceding claims, characterized in that the functional unit (9) comprises a low-pass filter (II) with a cut-off frequency between 10 and 100 Hz.
7. Safety circuit according to any one of the preceding claims, characterized in that the functional unit (9) comprises a high-pass filter (I) with a cut-off frequency between 0.5 and 10 Hz.
8. Safety circuit according to any one of the preceding claims, characterized in that the datum point for calculation of the control signal (Θ) is definable at the moment when the electric drive (2) is switched on.
9. Safety circuit according to any one of the preceding claims, characterized in that the functional unit (9') is realized by software algorithms of a microcontroller.
10. Safety circuit according to any one of the preceding claims, characterized in that the current path of an electric drive (2) is interruptible via a controllable power switch (5) by the control signal (Θ) generated in the comparing element (8) following comparison of the measured value (M, M') with a predetermined threshold value (S), and/or (optionally) the power flow from the electric drive (2) to a tool spindle (3) is simultaneously interruptible by a controllable clutch unit (4).

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