METHOD FOR OPERATING A HAND-GUIDED MACHINE TOOL, AND HAND-HELD MACHINE TOOL

Abstract

A method for operating a hand-guided machine tool. The method contains detecting at least one linear acceleration value by means of the at least one sensor apparatus (6); subtracting the gravitational acceleration from the at least one linear acceleration value to form an adjusted linear acceleration value; integrating the adjusted linear acceleration value into a speed value; integrating the speed value into a distance value; multiplying the speed value by a time constant to form at least one further distance value; adding the distance value to the further distance value to form at least one total distance value; filtering at least one of the linear acceleration values and/or at least one of the speed values; comparing the total distance value with a defined limit value; and initiating a predefined action when the total distance value exceeds the defined limit value. A hand-held machine tool for carrying out such a method is also described.

Claims

1-12. (canceled)

13: A method for operating a hand-guided machine tool connectable to a tool, with a drive for driving the tool, a control device and at least one sensor being provided, the sensor having a distance from a reference point associated with the machine tool or the tool greater than or equal to zero, the method comprising the steps of: detecting at least one linear acceleration value (a.sub.x, a.sub.y, a.sub.z) via the at least one sensor; subtracting a gravitational acceleration from the at least one linear acceleration value (a.sub.x, a.sub.y, a.sub.z) to form at least one adjusted linear acceleration value (a.sub.xkorr, a.sub.ykorr, a.sub.zkorr), integrating the at least one adjusted linear acceleration value (a.sub.xkorr, a.sub.ykorr, a.sub.zkorr) into at least one speed value; integrating the at least one speed value into at least one distance value (s.sub.x, s.sub.y, s.sub.z); multiplying the at least one speed value by a time constant (τ) to form at least one further distance value; adding the at least one distance value to the at least one further distance value to form at least one total distance value (s.sub.x, s.sub.y, s.sub.z); filtering at least one of the linear acceleration values or adjusted linear acceleration values (a.sub.x, a.sub.y, a.sub.z, a.sub.xkorr, a.sub.ykorr, a.sub.zkorr) or at least one of the speed values; comparing the at least one total distance value (s.sub.x, s.sub.y, s.sub.z) with a defined limit value; and initiating a predefined action when the at least one total distance value exceeds the defined limit value.

14: The method as recited in claim 13 further comprising determining at least one rotational rate value (ω.sub.x, ω.sub.y, ω.sub.z) from the at least one sensor, the rotational rate value (ω.sub.x, ω.sub.y, ω.sub.z) being multiplied by a value corresponding to the distance of the at least one sensor from the reference point, the determined rotational rate value being used to determine the total distance value (s.sub.x, s.sub.y, s.sub.z).

15: The method as recited in claim 13 wherein the at least one sensor determines linear acceleration values (a.sub.x, a.sub.y, a.sub.z) or rotational rate values (ω.sub.x, ω.sub.y, ω.sub.z) in at least two spatial directions

16: The method as recited in claim 15 wherein the at least one sensor determines linear acceleration values (a.sub.x, a.sub.y, a.sub.z) or rotational rate values (ω.sub.x, ω.sub.y, ω.sub.z) in at least three spatial directions.

17: The method as recited in claim 13 wherein an idle state of the machine tool in space is determined when a vector sum of the three linear acceleration values (a.sub.x, a.sub.y, a.sub.z) is within a defined range.

18: The method as recited in claim 17 wherein the defined range is from 8 m/s.sup.2 to 12 m/s.sup.2.

19: The method as recited in claim 13 wherein an idle state of the machine tool is determined on the basis of the three rotational rate values (ω.sub.y, ω.sub.y, ω.sub.z).

20: The method as recited in claim 19 wherein the idle state being determined, when a dot product of the three rotational rate values (ω.sub.x, ω.sub.y, ω.sub.z) is less than a defined limit value of 4000 rad.sup.2/s.sup.2.

21: The method as recited in claim 20 wherein the idle state being determined, when the dot product of the three rotational rate values (ω.sub.x, ω.sub.y, ω.sub.z) is less than a defined limit value of 2000 rad.sup.2/s.sup.2.

22: The method as recited in claim 13 wherein a position of the machine tool when the machine tool is in motion is determined on the basis of adding integrated rotational rate signals to the position of the machine tool in an idle state.

23: The method as recited in claim 13 wherein the time constant (τ) has a value between 5 and 150 ms.

24: The method as recited in claim 23 wherein the time constant (τ) has a value of 70 ms.

25: The method as recited in claim 13 wherein the at least one rotational rate value (ω.sub.x, ω.sub.y, ω.sub.z) or the at least one linear acceleration value (a.sub.x, a.sub.y, a.sub.z, a.sub.xcorr, a.sub.ykorr, a.sub.zkorr) is filtered in order to block a frequency value below a predetermined frequency threshold value or above a further frequency threshold value.

26: The method as recited in claim 13 wherein the predefined action corresponds to switching off or actively braking the drive, sending out a warning signal or outputting a signal on a display apparatus.

27: A hand-held machine tool connectable to a tool, comprising: a drive for driving the tool; a control device; and at least one sensor having a distance from a reference point associated with the machine tool or the tool greater than or equal to zero, the hand-held machine tool operable to carry out the method as recited in claim 13.

28: The hand-held machine tool as recited in claim 27 further comprising least one filter for blocking frequency values below a predetermined frequency threshold value or for blocking frequency values above a predetermined frequency threshold value is provided.

29: The hand-held machine tool as recited in claim 27 wherein the at least one sensor includes an acceleration sensor or a gyro sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Further advantages can be found in the following description of the drawings. Various embodiments of the present invention are shown in the drawings. The drawings, the description and the claims contain numerous features in combination. A person skilled in the art will expediently also consider the features individually and combine them to form meaningful further combinations.

[0037] In the drawings, identical and equivalent components are provided with the same reference signs. In the drawings:

[0038] FIG. 1 schematically shows a hand-held machine tool designed as an angle grinder in a perspective view;

[0039] FIG. 2 schematically shows the angle grinder according to FIG. 1 in a side view;

[0040] FIG. 3 schematically shows the angle grinder according to FIGS. 1 and 2 in plan view;

[0041] FIG. 4 is a simplified plan view of an alternative embodiment of a hand-held machine tool designed as an angle grinder, in which linear acceleration values and rotational rate values which can be determined by a sensor apparatus are visible;

[0042] FIG. 5 is a further simplified view of a hand-held machine tool designed as an angle grinder; and

[0043] FIG. 6 is a flow chart for graphical representation of the method according to the invention.

DETAILED DESCRIPTION

[0044] FIG. 1 shows a hand-held machine tool 1 or a hand-guided machine tool according to the invention which is designed as an angle grinder in the illustration shown. According to an alternative embodiment, the hand-held machine tool 1 can also be designed as a drill, as a hammer drill, as a chiseling hammer drill or as a saw, such as a circular saw, a jigsaw, a saber saw or the like.

[0045] The hand-held machine tool 1 designed as an angle grinder in the figures has a housing 2 and a tool 3, for example designed as a cutting disc. The housing 2 preferably has at least one holding region at which a user can hold and guide the hand-held machine tool 1 using one or both hands. The tool 3 can be actuated by a drive which can be supplied with current in particular by means of an accumulator which can be connected to the hand-held machine tool 1. According to an alternative embodiment, the hand-held machine tool 1 can also be supplied with electrical current from a network by means of a power cable.

[0046] The drive for actuating the tool 3 in a rotating, axial, gyrating or similar movement is arranged in the interior of the housing 2 along with a gear mechanism and a drive shaft 4. The drive, for example an electric motor, the gear mechanism and the drive shaft 4 are arranged in the housing 2 with respect to one another and connected to one another in such a way that a torque generated by the electric motor can be transmitted to the gear mechanism and finally to the drive shaft 4. A freely rotating end of the drive shaft 4 that projects downward on the housing 2 is connected to the cutting disc 3. The torque of the drive shaft 4 can thus be transmitted to the cutting disc 3, such that the cutting disc 3—as shown in FIG. 3—can rotate in the direction of the arrow R. The drive which is designed as an electric motor, the gear mechanism and the majority of the drive shaft 4 are not shown in the drawings.

[0047] The hand-held machine tool 1 also has a control device 5 and a sensor apparatus 6. The sensor apparatus 6 is connected to the control device 5 electrically or alternatively wirelessly, for example via radio. Signals can be sent between the sensor apparatus 6 and the control device 5. The control device 5 is in turn connected to the electric motor and the accumulator electrically or alternatively wirelessly, for example via radio. Signals can be sent between the sensor apparatus 6 and the electric motor and the accumulator. The control device 5 is used, inter alia, for open-loop and closed-loop control of the drive and the power supply of the hand-held machine tool 1.

[0048] In the present case, a single sensor apparatus 6 is provided. In an alternative embodiment, different sensor apparatuses can also be provided. In the present case, the sensor apparatus 6 is used to simultaneously detect six individual measurement values. In the present case, the sensor apparatus 6 is designed as a combined acceleration and/or gyro sensor. In alternative embodiments, it may also be the case that only one acceleration sensor or a separate acceleration sensor and a gyro sensor are provided, it being possible for the sensors in the last embodiment to be arranged at different locations of the machine tool 1.

[0049] In the present case, the sensor apparatus 6 is designed to detect a first linear acceleration value a.sub.x in a direction x, a second linear acceleration value a.sub.y in a direction y and a third linear acceleration value a.sub.z in a direction z. Furthermore, the sensor apparatus 6 is designed to detect a first rotational rate value or rotational speed value ω.sub.x in the rotational direction a about the rotational axis x, a second rotational rate value or rotational speed value ω.sub.y in the rotational direction b about the rotational axis y and a third rotational rate value or rotational speed value ω.sub.z in the rotational direction c about the rotational axis z.

[0050] If the tool 3 designed as a cutting disc remains stuck in a material to be machined, for example concrete, while working with the hand-held machine tool 1 and therefore the tool 3 no longer rotates relative to the material, the torque generated by the electric motor now acts on the housing 2 of the hand-held machine tool 1. As a result, the housing 2 begins to accelerate in the rotational direction N or counter to the rotational direction b. Such a sudden acceleration or sudden swing of the housing 2 of the hand-held machine tool 1 can be dangerous for a user.

[0051] In order to prevent a rotating disk from injuring the user or others, the control device 5 switches the electric motor off as quickly as possible when a sudden acceleration or sudden swing of the housing 2 of the hand-held machine tool 1 is detected with the aid of the values detected by sensor apparatus 6 and an algorithm which is stored in the control device 5 and is described by the method according to the invention.

[0052] A rotational axis of the tool 3 is defined here as the reference point P for which the respective present values are determined. In alternative embodiments and also in other types of hand-held machine tools, different reference points can be defined.

[0053] As can be seen from FIGS. 1 to 3, the sensor apparatus 6 in the present case is positioned, considered substantially in the longitudinal direction x of the hand-held machine tool 1, in the center of the housing 2 of the hand-held machine tool 1. In the present case, the reference point P thus has a distance D or r.sub.D from the sensor apparatus 6 in the longitudinal direction x of the hand-held machine tool 1.

[0054] In the embodiment according to FIG. 4, the sensor apparatus 6 for determining the linear acceleration values a.sub.x, a.sub.y, and a.sub.x is arranged at a first distance r.sub.D from the reference point P and a further sensor apparatus for determining the rotational rate values ω.sub.x, ω.sub.y, and ω.sub.z is arranged at a distance r.sub.D+r.sub.S from the reference point P.

[0055] In a further alternative embodiment of the invention, it can be provided that a distance between the reference point P and the sensor apparatus 6 is equal to zero and the sensor apparatus 6 is thus arranged in the reference point P.

[0056] A method is first described below which is applied when the sensor apparatus 6 is arranged in the reference point P.

[0057] The sensor apparatus 6 detects a first linear acceleration value a.sub.x in a direction x, a second linear acceleration value a.sub.y in a direction y and a third linear acceleration value a.sub.z in a direction z. The directions x, y and z are in each case perpendicular to one another, the x direction corresponding, for example, to the longitudinal direction of the hand-held machine tool 1, the y direction corresponding to a vertical direction of the hand-held machine tool 1 and the z direction corresponding to a transverse direction of the hand-held machine tool 1.

[0058] The first, second and third linear acceleration value a.sub.x, a.sub.y, a.sub.z is detected after the drive of the hand-held machine tool 1 has been activated and a torque is transmitted to the tool 3 designed as a cutting disc.

[0059] The gravitational acceleration (g=9.81 m/s.sup.2) which is additionally detected by the sensor apparatus 6 acts permanently on the hand-held machine tool 1. Since this is disruptive for determining a critical state of the hand-held machine tool 1, the relevant component of the gravitational acceleration value g is deducted from the first, second and third linear acceleration value a.sub.x, a.sub.y, a.sub.z and thereby a fourth, fifth and sixth acceleration value a.sub.xcorr, a.sub.ykorr, a.sub.zkorr is determined.

[0060] In order to be able to subtract the gravitational acceleration from the linear acceleration values a.sub.x, a.sub.y, a.sub.z, for example in a vector calculation, it is necessary to know the position or orientation of the hand-held machine tool 1 in free space.

[0061] In the idle state of the hand-held machine tool 1, the orientation of the hand-held machine tool 1 in free space is determined directly by the linear acceleration values a.sub.x, a.sub.y, a.sub.z which are detected by the sensor apparatus 6. In this case, the only acceleration value which can be detected by the sensor apparatus 6 is the gravitational acceleration value g. Because the gravitational acceleration is directed substantially to the center of the earth, the control device 5 can be used to determine the orientation or position of the hand-held machine tool 1 in free space in relation to the direction in which the gravitational acceleration acts.

[0062] A state in which a sum of the three linear acceleration values a.sub.x, a.sub.y, a.sub.z lies within a defined range of from 8 m/s.sup.2 to 12 m/s.sup.2, for example, is defined as the idle state of the hand-held machine tool 1. Alternatively, in order to reduce computing power, a dot product of the linear acceleration values a.sub.x, a.sub.y, a.sub.z can be used together with a correspondingly adjusted range.

[0063] As an alternative or in particular in addition to this, an idle state of the hand-held machine tool 1 can be determined on the basis of rotational rate values ω.sub.x, ω.sub.y and ω.sub.z which are determined by the sensor apparatus 6, an idle state being determined, for example, when a dot product of the three rotational rate values is less than a defined limit value of 4000 rad.sup.2/s.sup.2, in particular less than approximately 2000 rad.sup.2/s.sup.2, for example.

[0064] If an idle state of the hand-held machine tool 1 is not detected, a position of the hand-held machine tool 1 is determined on the basis of adding integrated rotational rate signals ω.sub.x, ω.sub.y and ω.sub.z to the position of the hand-held machine tool 1 in the last determined idle state. Such a determination of the position of the hand-held machine tool 1 is continued until the hand-held machine tool 1 is again determined to be in an idle state. The position of the hand-held machine tool 1 is then determined again on the basis of the linear acceleration values a.sub.x, a.sub.y, a.sub.z.

[0065] In the next step, the fourth, fifth and sixth corrected acceleration value a.sub.xkorr, a.sub.ykorr, a.sub.zkorr are integrated into a first, second and third speed value or linear speed value.

[0066] The first, second and third speed value are subsequently integrated and a first, second and third distance value are determined.

[0067] In particular in parallel with this, the first, second and third speed value are multiplied by a time constant τ and a fourth, fifth and sixth distance value are determined. The time constant can be a fixed period of time between 10 ms and 100 ms, in particular of approximately 70 ms.

[0068] Finally, the first, second, third, fourth, fifth and sixth distance values are added to determine a total distance value.

[0069] By means of the control device 5, a predefined action is initiated if the total distance value exceeds a predetermined limit value GW. This is shown in simplified form in FIG. 5, in which the predefined limit value GW is shown schematically in an axis in the form of a circle about the drive axis of the tool 3, the predefined action being initiated if the position of the reference point P that is predicted by the control device 6 at a defined point in time lies outside the circle GW. When considering all three spatial axes x, y and z, the predefined limit value GW could represent a sphere, for example. It can be provided that the limit values in the three spatial axes x, y and z differ from one another.

[0070] If the predefined limit value GW is exceeded, the drive of the hand-held machine tool 1 is braked by the control device 5, in particular by sending out a corresponding signal to the drive. Braking the drive prevents the tool 3 rotating here from injuring a user of the hand-held machine tool 1.

[0071] In an embodiment in which the sensor apparatus 6 is arranged so as to be spaced apart from the reference point P, the rotational rate values or signals ω.sub.x, ω.sub.y and ω.sub.z are also used, in addition to the method described above, to also have an effect on a possible rotation of the hand-held machine tool 1 at the reference point P.

[0072] The rotational rate values ω.sub.x, ω.sub.y and ω.sub.z are detected by the sensor apparatus 6. The first rotational rate value ω.sub.x is the rotational speed at which the hand-held machine tool 1 rotates about the rotational axis x in the rotational direction a. The second rotational rate value ω.sub.y is the rotational speed at which the hand-held machine tool 1 rotates about the rotational axis y in the rotational direction b. The third rotational rate value ω.sub.z is the rotational speed at which the hand-held machine tool 1 rotates about the rotational axis z in the rotational direction c. It is of course also possible that the hand-held machine tool 1 can rotate counter to the rotational direction a, b or c.

[0073] In the present case, the reference point P lies in the center of the cutting disc 3 and thus in the sensor axis x, such that the rotational rate values ω.sub.x need not be taken into account for calculating the respective distance values s.sub.x, s.sub.y and s.sub.z. The position of the reference point P is determined by means of a double integration of the accelerations added to an integration of the rotational rates multiplied by the distance D or r.sub.D of the sensor apparatus 6 from the reference point P. The respective distance values s.sub.x, s.sub.y and s.sub.z can therefore be calculated according to the embodiment in FIG. 4 as follows:

s.sub.z=∫(r.sub.D.Math.ω.sub.ySensor+∫a.sub.zSensordt)dt

s.sub.y=∫(r.sub.D.Math.ω.sub.zSensor+∫a.sub.ySensordt)dt

s.sub.x=∫∫a.sub.xSensordt

[0074] If the sensor apparatus 6 does not lie in the sensor axis x, the respective rotational rate values ω.sub.x must also be taken into account when determining the distance values s.sub.x, s.sub.y and s.sub.z, as is shown below by way of example for the distance value s.sub.z:

s.sub.z=∫(r.sub.D.Math.ω.sub.ySensor+r.sub.D2.Math.ω.sub.xSensor∫a.sub.zSensordt)dt

[0075] The first, second and third rotational rate value ω.sub.x, ω.sub.y and ω.sub.z is multiplied, according to the diagram shown in FIG. 6, by the relevant distance value D or r.sub.D in order to determine a further speed value in the form of a fourth, fifth and sixth speed value. As already mentioned above, the relevant distance value D or r.sub.D corresponds to a distance between the sensor apparatus 6 and the reference point P in the relevant spatial direction x, y or z.

[0076] In a subsequent step, according to the diagram shown in FIG. 6, the further speed values which are determined from the rotational rate values ω.sub.x, ω.sub.y and ω.sub.z are added to the speed values which are determined from the acceleration values to form respective overall speed values and these are used to determine the distance values, as described in more detail above, in order to ascertain if the limit value has been exceeded.

[0077] In order to calculate the position of the hand-held machine tool 1 by the time τ in advance, the following calculations are carried out overall for the individual directions, for example:

s.sub.z=∫(r.sub.D.Math.ω.sub.ySensor+∫a.sub.zSensordt)dt+τ(r.sub.D.Math.ω.sub.ySensor+∫a.sub.zSensordt)

s.sub.y=∫(r.sub.D.Math.ω.sub.zSensor+∫a.sub.ySensordt)dt+τ(r.sub.D.Math.ω.sub.zSensor+∫a.sub.ySensordt)

s.sub.x=∫∫a.sub.xSensordt+τ.Math.∫a.sub.xSensordt

[0078] In a further step, a total distance value is determined from the determined coordinates and this is compared with the defined limit value GW. If the total distance value is greater than the defined limit value GW and the reference point P at the current time added to the time constant τ would be outside the defined limit value GW, the drive is actively braked in the present case. Otherwise the operation continues unchanged.

[0079] When the hand-held machine tool 1 is in operation, i.e. during grinding, cutting, sawing, drilling or the like for example, disruptions, such as strong vibrations, can occur which can lead to unwanted switching-off of the hand-held machine tool 1. In order to be able to avoid this in a simple manner, the measured acceleration values are filtered. For example, a low-pass filter can be provided, with typical frequencies for low-pass filtering being between 0.1 Hz and 6 Hz, in particular approximately 1 Hz. In hand-held machine tools 1 which have in particular oscillating tools 3, such as saws, interference signals can have an influence on the rotational rate values, it being possible for said values to be filtered out using a low-pass or bandpass filter. The frequency of these filters is adapted to the frequency of the oscillating movement, such that said filters are damped to the desired extent.

[0080] In general, at least one rotational rate value ω.sub.x, ω.sub.y and ω.sub.z and/or at least one linear acceleration value a.sub.x, a.sub.y, a.sub.z, a.sub.xkorr, a.sub.ykorr, a.sub.zkorr can be filtered in order to block frequency values which are below a predetermined frequency threshold value and/or above a further frequency threshold value. For example, this makes it possible for even minor movements of the hand-guided machine tool that are not caused by a stuck tool to be disregarded for the method.

[0081] The filter can be a high-pass filter, a low-pass filter or a band-limited filter. It has proven to be advantageous if a band-limited filter is used both for the acceleration values a.sub.x, a.sub.y, a.sub.z and for the speed values, the limit frequencies preferably being approximately 0.5 Hz and 10 Hz, in particular approximately 2.8 Hz. The values can be filtered in each case before or after the speed values generated from the linear acceleration values a.sub.x, a.sub.y, a.sub.z are combined with the speed values calculated from the rotational rate values ω.sub.x, ω.sub.y and ω.sub.z. Particularly good results can be achieved if a band-limited filter is used for the linear acceleration values a.sub.x, a.sub.y, a.sub.z and a high-pass filter is used for the rotational rate values ω.sub.x, ω.sub.y and ω.sub.z or a band-limited filter of the speed values is used before or after a combination of the signals.