EP3363598A1 - Method for braking a tool spindle - Google Patents

Abstract

The invention relates to a method for braking a tool spindle (2) of a power tool (1), comprising the following steps:
- Determining a locking state of a tool (3) on the tool spindle (2) by a sensor arrangement (5);
Selecting a time braking torque function and / or a maximum braking torque (M _B1 , M _B2 ) on the basis of the determined locking state; and
- Braking the tool spindle (2) by a brake assembly (4) according to the selected time-braking torque function and / or such that the selected maximum braking torque (M _B1 , M _B2 ) is not exceeded.

Description

The invention relates to a method for braking a tool spindle of a power tool and a power tool comprising a tool spindle. Furthermore, the invention relates to a computer program with program code means to perform a method for braking a tool spindle.

Electric machine tools whose tool spindle requires a tool to be replaced from time to time, in particular due to wear, have been known for a long time. For safe operation, it is necessary to attach the tool sufficiently fixed to the tool spindle.

In order to improve the comfort and reliability of such power tool machines, tool-free clamping devices have become known. Such clamping devices, be exemplary on the DE 20 2009 000 482 U1 referenced, are designed such that the clamping device on the tool spindle during operation of the power tool on its own tightening. It is usually sufficient if the user only tightens the tool on the tool spindle. The clamping devices are designed so that they can not solve themselves in the normal operation of the power tool. Such power tool machines are popular with the user because of their ease of use and the associated improved reliability.

Also, to improve the reliability of electric power tools are now increasingly equipped with brake assemblies for braking the tool spindle. Without such a brake assembly, the tool would continue to rotate for a comparatively long time after switching off the power tool due to inertia. The even after the completion of work with the power tool further rotating tool can in a row pose a high risk of injury to the user if the user does not take special care in the use of the power tool. Furthermore, there is a risk with the power tool by the still rotating tool to damage other objects, for example, scratch when the power tool is discarded carelessly.

In order to minimize the risk potential of the power tool, is for example in the EP 2 947 765 A2 discloses an electronic brake assembly for a universal motor of a power tool. The brake assembly is capable of braking the engine of the power tool when the power tool is to be turned off.

Finally, a particularly safe and convenient power tool can be provided by simultaneously equipping a power tool with a tool-less tensioner and with a brake assembly.

In the sudden deceleration of the tool spindle, however, there is the problem that due to the inertia of the tool this would like to move on with the remaining momentum and transmits this moment of inertia to the clamping device, which is to fix the tool to the tool spindle. It is problematic that the moment of inertia of the tool in its direction of the tightening direction of the clamping device is directed exactly opposite. Thus, the momentum of the tool causes a release movement of the clamping device, resulting in a significant risk to the user. In the worst case, the tool can thus run off the tool spindle and represent a very significant risk.

The first prior art approaches to this problem are already known. For example, the EP 2 632 635 B1 a flow control device for avoiding the running of a clamping element and / or a tool from a tool spindle in a braking operation with at least one transmission unit, wherein the transmission unit comprises a first transmission element, a second transmission element movable relative to the first transmission element and a movement changing unit which is provided, in the braking operation, a first relative movement between the first transmission element and the second transmission element to convert into a second relative movement. It is proposed that the flow control device has at least one imbalance compensation unit which is provided to at least reduce the imbalance of the transmission unit in an operating state, wherein the imbalance compensation unit has at least one imbalance compensation element which is movably mounted in the first transmission element of the transmission unit.

In particular, if a tool-free locking of the tool is provided on the tool spindle, care must be taken with a slow down of the tool spindle. This is especially true because it can not be guaranteed that the self-tightening clamping device and the attached tool already have sufficiently fixed to the tool spindle.

In order to ensure sufficient reliability in any case, either complicated and thus costly mechanical structures or means must be provided within the clamping device, similar to the EP 2 632 635 B1 disclosed, or to dispense with the safety-related function of the automatic deceleration.

A satisfactory solution to the problem, especially for a power tool with tool-free fixation of the tool in combination with a spindle brake, currently does not exist.

The present invention has for its object to provide an improved method for braking a tool spindle of a power tool in which in particular a reliable braking while maintaining simple design means is always guaranteed. The present invention is also based on the object to provide a comparison with the prior art improved power tool.

As a solution in the present invention, a method for braking a tool spindle with the features listed in claim 1, a power tool with the features listed in claim 11 and a computer program with program code means according to the features listed in claim 15 proposed. The dependent claims and the features described below relate to advantageous embodiments and variants of the invention.

• Ermitteln eines Arretierzustands eines Werkzeugs an der Werkzeugspindel durch eine Sensoranordnung;
• Auswählen einer Zeit-Bremsmoment-Funktion und/oder eines maximalen Bremsmoments auf Basis des ermittelten Arretierzustands; und
• Abbremsen der Werkzeugspindel durch eine (elektrische) Bremsanordnung gemäß der ausgewählten Zeit-Bremsmoment-Funktion und/oder derart, dass das ausgewählte maximale Bremsmoment nicht überschritten wird.

The method according to the invention for braking a tool spindle of a power tool comprises the following steps:

• Determining a locking state of a tool on the tool spindle by a sensor arrangement;
• Selecting a time-braking torque function and / or a maximum braking torque on the basis of the determined locking state; and
• Braking the tool spindle by an (electric) brake assembly according to the selected time-braking torque function and / or such that the selected maximum braking torque is not exceeded.

By determining the Arretierzustands should be determined whether and how firm or how safe the tool is attached to the tool spindle. Thus, for example, the tightening torque of the tool is determined on the tool spindle or a clamping device which fixes the tool to the tool spindle. It can be distinguished at least between a state in which the Tool is reliably locked to the tool spindle and thus there is no risk of unwanted inertial release of the tool when braking the tool spindle, and a state in which the tool is not locked in this way on the tool spindle.

The fact that the braking takes place in accordance with a selected time-braking torque function and / or taking into account a maximum braking torque, resulting for the tool spindle differently shaped so-called. Braking ramps. A deceleration ramp is a decaying time operating torque function, thus representing the reduction in operating speed over time during a braking event. A steep deceleration ramp results in rapid deceleration (i.e., a rapid reduction in operating speed) of the tool spindle; a slow brake ramp to slow deceleration (i.e., a slow decrease in operating speed). Basically, a large braking torque results in a steep braking ramp and a low braking torque results in a flat braking ramp. It can thus be provided to selectively select a braking ramp by selecting a time-braking torque function and / or a maximum braking torque.

The braking process can be controlled such that a previously selected time-braking torque function and / or a maximum braking torque and / or a desired braking ramp are traversed or maintained.

By braking the tool spindle on the basis of the previously determined locking state can be ensured that the tool spindle is always maximally or optimally braked depending on the Arretierzustands of the tool, ie as quickly as possible, but only to the extent that a release of the tool the tool spindle or a release of the clamping device is just avoided. If the tool is therefore fixed sufficiently strong on the tool spindle, for example, the highest possible braking torque be introduced during the braking process. With a loose or insufficiently locked tool, on the other hand, braking can be completely dispensed with or the tool spindle can only be subjected to a reduced braking torque. Of course, any number of gradations between these extremes are possible. The tool spindle is thus always braked as fast as the locking state just allows. As a result, maximum operational safety and maximum comfort can be guaranteed. On technically complex designed clamping devices that prevent the release of the tool during braking in a mechanical manner, can be dispensed with.

In one embodiment of the invention, a tool-free locking of the tool on the tool spindle, in particular a self-locking when driving or accelerating the tool, can be provided.

In particular, a clamping device can be provided for tool-free axial clamping of a disc-shaped tool. The disclosure of the DE 20 2009 000 482 U1 incorporating such a tensioner, is hereby fully incorporated by reference into the present specification by reference. Such a clamping device is also referred to as a Quickmutter or clamping nut.

The invention is in principle equally suitable for a power tool in which a manual locking of the tool is provided on the tool spindle, and for a power tool with self-locking. The invention for a power tool with self-locking particularly useful because the user in this case has no direct control of a sufficient locking of the tool on the tool spindle and thus must rely on the self-locking and ensuring safety in a deceleration.

In a further development of the invention can be provided that the sensor arrangement, the locking state by monitoring a locking force of the tool on the tool spindle, an imbalance of the driven and braked tool, an achieved before braking operating speed of the tool spindle, achieved before braking angular acceleration of the tool spindle and / or a power consumption and / or power consumption of the power tool machine achieved before braking.

All these parameters alone or in combination with each other make it possible to draw conclusions about the locking state. The above list is not exhaustive and a choice of one or more options for determining the locking state can be made by a person skilled in the art, taking into account the available means, in particular the existing sensors, of a power tool.

For example, when using a force sensor and / or pressure sensor, the locking force of the tool on the tool spindle or the locking of the clamping device and thus the locking state can be determined directly without major detours.

Furthermore, it can also be provided, for example, using at least one acceleration sensor or a vibration sensor, to detect an imbalance or a troubled run of the tool, which can for example indicate a loose locking state of the tool on the tool spindle, the z. B. can make noticeable by excessive vibration of the tool.

It is also conceivable that a determination of the locking state by monitoring an achieved operating speed and / or angular acceleration of the tool spindle and / or an achieved power consumption and / or power consumption the power tool is at the time before the deceleration of the tool spindle. The method can thereby be easily implemented without expanding the sensor technology of the power tool, since the power tool usually already provides means or sensors to monitor the operating speed, angular acceleration, power consumption and / or power consumption.

Since a self-tightening of the tool on the tool spindle is achieved in particular by the moment of inertia of the tool during the acceleration process of the tool spindle, by monitoring the angular acceleration of the tool spindle can be concluded indirectly on a locking state of the tool. Also by monitoring the operating speed, a conclusion can be drawn on the locking state of the tool, since the usual acceleration data of the power tool to reach the operating speed or at least statistical data / estimates on the relationships between reached maximum operating speed since the last start of the tool spindle and the locking state of the tool are known. Furthermore, when monitoring the operating speed over a certain period of time, mathematical differentiation can be used to deduce the angular acceleration of the tool spindle, for example in accordance with the relationship: $$\mathrm{a}\left(\mathrm{t}\right)=\mathrm{dw}/\mathrm{dt}=\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="imgf0001.png"\; state="\{\{state\}\}">d</figure-callout>}\left(\mathrm{2}\mathrm{\pi }\cdot \mathrm{rpm}\left(\mathrm{t}\right)\right)/\mathrm{dt}\mathrm{,}$$

Finally, it can also be concluded by monitoring the power consumption and / or power consumption on an operating speed and / or acceleration of the tool spindle.

It can be provided to continuously determine the locking state of the tool of a tool spindle. Alternatively, it can also be provided to determine the locking state of the tool of a tool spindle in discrete steps.

As mentioned above, it may be provided, for example, that one of at least two possible locking states is determined, preferably an unlocked state of the tool on the tool spindle, and a locked state of the tool on the tool spindle.

The binary determination of a locking state (not locked / locked) can be technically simple and thus economically feasible. Due to the great contrast between the two locking states, the detection is also extremely reliable and robust. It has been found that, in particular when using a self-tightening clamping device or a self-tightening clamping device, a tool is in practice either only weakly locked fixed to the tool spindle, for example when the power tool is not or only very briefly, for example accidentally, was put into operation, or sufficiently strong locked as soon as the power tool has been operated significantly. The detection of more than two locking states is thus usually not required in practice, but may still be advantageous in some cases.

The expression "locked state" of the tool is not necessarily to refer to the binary state not locked / locked below. With a "locked state" of the tool may hereinafter also be meant one or more of many locking states in which the tool already has a certain lock, for example (based on a maximum lock) 20% locking, 40% locking, 60% locking, 80% locking or 100% locking.

In a further development of the invention it can be provided that the sensor arrangement monitors a starting process of the power tool and determines a locked state of the tool on the tool spindle, if during the startup process at least a predetermined uninterrupted acceleration process of the tool spindle has taken place.

In particular, the course of the operating speed over the time from the actuation of the operating switch (or from the switch-on, respectively) of the electric power tool is meant by a starting operation of the power tool. In particular, when starting the power tool, a self-locking of the tool on the tool spindle can take place due to the inertia of the tool. The Selbstarretierung usually takes place particularly well when an uninterrupted acceleration process for a certain time, d. H. a substantially steady increase in the operating speed of the tool spindle for a certain time occurs. Thus, for example, the tool may not be sufficiently locked when the user "plays" only with the power tool power switch, i. H. at short intervals, the power tool on and off. The inventors have recognized that a power tool can be brought to high operating speed by such a pulsating operation of the operating switch, but the tool is then regularly not sufficiently locked. By specifying an interruption-free acceleration process for a certain predetermined period of time, which can be determined by the person skilled in the art for the particular electric machine tool, a criterion for detecting the locking state can thus be found.

In one embodiment of the invention may also be provided that a threshold value for a speed change of the tool spindle and / or a threshold for a power consumption and / or power consumption of the power tool is used or, in the case of which or exceeding a locked state of the tool the tool spindle is determined.

Accordingly, the differentiation of the locking states can take place by appropriately selecting a threshold value (or several threshold values) with respect to the parameter (s) determined or detected with the sensor (s).

It is technically easy to detect a locking state by using a threshold value, which, of course, can be used for any monitored parameters of the power tool that are indicative of a locking of the tool on the tool spindle. Of course, a plurality of threshold values may be provided for the same parameter, for example for the speed change. Of course, it is also possible to provide a single threshold value for one assigned parameter each, exceeding which, for example, a locked state of the tool is detected and, if it is undershot, an unlocked state of the tool on the tool spindle.

By way of example, a first threshold value can be provided for a parameter which, when exceeded, results in a locked state of the tool, whereby when the value falls below a second threshold value, an unlocked state of the tool is detected. Thus, the detection of an intermediate state and thus a third Arretierzustands would be possible.

It is also possible to merge several monitors / sensors with respect to different parameters with one or more threshold values per parameter.

In one development of the invention it can be provided that the sensor arrangement monitors an operating process of the power tool and determines a locked state of the tool on the tool spindle when the power tool has been operated.

It has been found that the tool, in particular when using a self-locking device, for example in the form of a self-tightening clamping nut, can also be tightened against the tool spindle during an operating process of the power tool machine. Under an operation will be below not only understood the pure startup process of the electric machine tool, but rather a process by which a user of the power tool has already carried out particular manual work with the tool of the power tool. If, for example, the tool is held against a workpiece to be machined, it is thereby braked by the workpiece, while the tool spindle continues to rotate. In this way and due to the subsequent re-acceleration process of the tool (as soon as it has disengaged from the workpiece), the tool is tightened on the tool spindle. Thus, by monitoring an operating procedure or by monitoring whether such an operating process has taken place, the locking state of the tool on the tool spindle can be determined.

In particular, it can be concluded that an operation has taken place when it is monitored whether the power consumption and / or power consumption of the power tool has exceeded a predefined setpoint value or threshold value, and the operating speed of the tool spindle has exceeded a further threshold value. In this case, it can be safely assumed that a user has worked with the power tool or the tool.

In a further development of the invention it can be provided that the braking torque, which is introduced via the (electric) brake assembly on the tool spindle, is selected such that a previous drive torque, with which the tool spindle has been applied, is not exceeded.

The fact that the braking torque can be chosen such that it does not exceed a previous drive torque, it can be ensured that the tool is not spent in a less strong locking state, as before the commissioning of the power tool.

It may be advantageous that a minimum braking torque is always provided for each deceleration process, regardless of the determined locking state of the tool.

In a preferred development of the invention, it can be provided that exactly one maximum braking torque and / or exactly one time-braking torque function is assigned to each detectable locking state.

By such a direct assignment can always be ensured an optimal braking of the tool spindle in dependence of the locking state. The tool spindle is thus decelerated just as fast as operational safety permits.

Alternatively, it is also possible to assign a common maximum braking torque and / or a common time-braking torque function to a plurality of locking states. Furthermore, it is also within the meaning of the invention to use a mathematical relationship between the locking state and the maximum braking torque and / or the time-braking torque function or their parameters. As a result, in particular a stepless allocation can be possible.

In a further development of the invention may also be provided that a first maximum braking torque is used to decelerate the tool spindle when a locked state of the tool was determined on the tool spindle, and a second maximum braking torque is used to brake the tool spindle, if an unlocked Condition of the tool was determined on the tool spindle, wherein the first maximum braking torque is greater than the second maximum braking torque.

Particularly simple is the determination of two possible (binary) Arretierzuständen (not locked / locked), which corresponding braking torques (minimum braking torque / maximum braking torque) are assigned.

The invention also relates to a power tool, comprising a tool spindle, on which a tool can be locked, further comprising an electric drive arrangement for driving the tool spindle and an (electric) brake assembly for braking the tool spindle, and a sensor arrangement for determining a locking state of the tool on a tool spindle wherein the sensor assembly and the brake assembly are configured to perform the above method.

Features and advantages that have already been described for the process, of course, in the context of the power tool and implemented vice versa.

In particular, the brake assembly may be a brake assembly that is electrically controllable and / or controllable. The brake assembly is able to initiate at least two different deceleration processes or braking ramps into the tool spindle on the basis of at least one control signal. Depending on the embodiment, the braking force of the brake assembly can be continuously adjusted electrically.

The brake assembly may also be composed of a plurality of brake devices. For example, two brake devices may be provided, which are able to initiate different degrees of braking. Depending on the detected locking state then one of the brake devices, the other of the brake devices or both brake devices can be activated.

In a particularly preferred embodiment of the invention, a tool-free locking of the tool on the tool spindle, in particular a self-locking when driving or accelerating the tool, may be provided.

As already mentioned above, the invention is suitable for a power tool, in which a manual locking of the tool is provided on the tool spindle and for a power tool with Selbstarretierung alike. Particularly preferred for use is the invention for a power tool with Selbstarretierung.

In one embodiment of the invention may also be provided that an electric drive assembly, in particular a DC motor or single-phase series motor (also referred to as a universal motor), can be used as part of the brake assembly to introduce a braking torque.

The drive assembly and the brake assembly may thus belong to the same assembly and even be identical. In particular, when using a DC motor or single-phase series motor can be done by the drive assembly without great technical effort, an electric braking.

Alternatively, however, it can also be provided that the drive arrangement and the brake arrangement are formed independently of one another. For example, a controllable disc brake or the like could be provided. A combination of several braking techniques and thus a distributed brake arrangement are within the meaning of the invention.

Although the invention for a drive assembly in the training as a DC motor or single-phase series motor can be used advantageously due to the then technically easy to implement combination of the drive assembly with the brake assembly, of course, any drive arrangement be provided. For example, three-phase motors can be provided, which are equipped with an additional braking function.

In general, means for countercurrent braking, regenerative braking, resistance braking, DC braking or other electrical methods may be provided.

A selection circuit may be provided between the sensor arrangement and the brake arrangement which selects a time-braking torque function and / or a maximum braking torque on the basis of at least one control signal of the sensor arrangement and forwards them to the brake arrangement. Within the selection circuit, for example, a multiplexer and / or a lookup table can be provided. The sensor arrangement may alternatively pass control signal (e) directly to the brake assembly.

In an embodiment of the invention can be provided that the power tool is designed as an angle grinder and / or the tool as a grinding wheel or are.

In principle, however, the power tool can be any power tool, for example an electric hand tool or a stand tool. In particular, the invention is suitable for machines with rotationally driven tools, such as angle grinders, circular saws and drills.

The invention also relates to a computer program with program code means to carry out the method described above, when the program is executed on a microprocessor of a computer, in particular on an electronic control and / or control device of the power tool described above.

Alternatively or additionally, the method can also be used on a programmable logic circuit, for. On a Field Programmable Gate Array (FPGA) or programmable logic array (PLA). Implementation in an application specific integrated circuit (ASIC) and / or by discrete analog and / or digital components arranged and connected on a printed circuit board is also possible.

Embodiments of the invention will be described in more detail with reference to the drawing.

The figures each show preferred embodiments in which individual features of the present invention are illustrated in combination with each other. Features of an exemplary embodiment can also be implemented independently of the other features of the same exemplary embodiment and can accordingly be readily connected by a person skilled in the art to further meaningful combinations and sub-combinations with features of other exemplary embodiments.

In the figures, functionally identical elements are provided with the same reference numerals.

Figur 1

eine isometrische Darstellung einer erfindungsgemäßen Elektrowerkzeugmaschine;

Figur 2

ein Schaltungsdiagramm für eine erfindungsgemäße Elektrowerkzeugmaschine;

Figur 3

eine aufgenommene Zeit-Betriebsdrehzahl-Funktion der Werkzeugspindel zur Ermittlung des Arretierzustands;

Figur 4

zwei beispielhafte Bremsrampen zum Abbremsen der Werkzeugspindel; und

Figur 5

eine Schaltungsanordnung zum Auswählen einer Zeit-Bremsmoment-Funktion.

They show schematically:

FIG. 1

an isometric view of a power tool according to the invention;

FIG. 2

a circuit diagram for a power tool according to the invention;

FIG. 3

a recorded time operating speed function of the tool spindle for determining the locking state;

FIG. 4

two exemplary brake ramps for braking the tool spindle; and

FIG. 5

a circuit arrangement for selecting a time-braking torque function.

FIG. 1 shows by way of example a power tool 1, to which the invention is applicable. In the present case, the power tool 1 is designed as an angle grinder 1 by way of example. The angle grinder 1 comprises a tool spindle 2 (compare schematically in FIG FIG. 2 ), on which a tool 3, in this case a grinding wheel 3, can be locked. Of course, the power tool 1 may be any power tool 1, for example, a stand tool, and the tool 3 may be any tool 3.

The electric machine tool 1 comprises an electric drive arrangement M (cf. FIG. 2 In the exemplary embodiment, it is provided that an electric motor M is used as the drive arrangement M, for example, a DC motor or a single-phase series motor, which is simultaneously used as a brake assembly 4, in order to drive the tool spindle 2 and a brake assembly 4 to decelerate the tool spindle to introduce a braking torque M _B1 , M _B2 . There are no additional means for forming the brake assembly 4 are provided in the embodiment thus.

The electric machine tool 1 further provides a sensor arrangement 5 (cf. FIG. 2 ) for determining a locking state of the tool 3 or the grinding wheel 3 on the tool spindle 2, wherein the sensor arrangement 5 and the brake assembly 4 perform a method described below for braking the tool spindle 2.

Preferably, a tool-free locking of the tool 3 on the tool spindle 2, in particular a self-locking when driving or accelerating the tool spindle 2, is provided. For this purpose, a (not shown) clamping device may be provided.

The method for braking the tool spindle 2 of the electric machine tool 1 is described below first with reference to the schematically illustrated circuit arrangement of FIG. 2 described.

In FIG. 2 is, in contrast to the mains powered embodiment of the FIG. 1 , a battery-powered power tool 1 shown. The electric machine tool 1 is powered by a battery pack 6, consisting of four individual battery cells 6.1, with electrical energy. The type of electrical power supply and the number of rechargeable batteries 6.1 when supplied by a battery pack 6, however, are irrelevant to the operating principle of the invention.

In the Figures 1 and 2 is a manually operable operation switch 7 is shown, via which a user can close or open the circuit between the battery pack 6 (or the power source) and the drive assembly M either. If the operating switch 7 or the circuit is closed, the drive assembly M is supplied with electrical energy and the power tool 1 starts a start-up process. The connection of the drive assembly M with the tool spindle 2 and the lockable on the tool spindle 2 tool 3 is in FIG. 2 only shown very schematically.

If the operating switch 7 is opened again by the user, it is provided to use the drive arrangement M for braking the tool spindle 2, for example by short-circuiting the motor windings thereof or driving the drive arrangement M in the reverse direction of rotation. It can Also, at least one mechanical brake be provided within the drive assembly M, which is electrically controlled and / or regulated or are.

In order to avoid that the tool 3 uncontrollably loosens or loosens in the case of braking due to the inertia of the tool 3 of the tool spindle 2, the inventive method for braking the tool spindle 2 can be used.

Initially, the locking state of the tool 3 on the tool spindle 2 is determined by the sensor arrangement 5. The locking state can be determined in various ways. In the embodiment of the FIG. 2 a current measuring device (ammeter) A is provided within the circuit, whereby the current consumption i and / or power consumption of the electric machine tool 1 can be determined prior to deceleration.

In addition, it is provided in the exemplary embodiment that, to determine the locking state, an operating rpm rpm of the tool spindle 2 reached before braking or an angular acceleration of the tool spindle 2 achieved before braking is determined. This is in FIG. 2 indicated in the form of the icon 8.

Alternatively or additionally, the locking state can also be detected directly by monitoring a locking force of the tool 3 on the tool spindle 2 or an imbalance of the driven or braked tool 3.

On the basis of the ascertained locking state, a time braking torque function and / or a maximum braking torque and thus a braking ramp are subsequently selected. For this purpose, a selection circuit 9 is provided in the embodiment. According to the selected time braking torque function and / or such that the selected maximum braking torque is not exceeded, the braking action of the tool spindle 2 is finally initiated by the brake assembly 4.

The inventors have recognized that a locking state of the tool 3 on the tool spindle 2 can be determined by monitoring a startup process of the power tool 1. In particular, it can be concluded that a locked state of the tool 3 on the tool spindle 2, if during the startup process at least a predetermined uninterrupted acceleration process of the tool spindle 2 has taken place. The facts should be based on FIG. 3 be clarified.

FIG. 3 shows by way of example a detected by the sensor assembly 5 time operating speed function rpm (t) of the tool spindle 2. It starts at time t ₀ a startup of the power tool 1 by the user closes the power switch 7 of the power tool 1 first. In the further course, until the time t ₁ , the user "plays" with the operating switch 7, whereby no continuous increase of the operating speed rpm takes place. It has been found that, in particular when using a power tool 1 with tool-free locking or self-locking as a result of such a start-up operation, the tool 3 is often not sufficiently locked to the tool spindle 2. From the time t ₁ , the user actuates the operating switch 7 of the electric machine tool 1, however, for a sufficiently long time (longer than the time t ₂ ), whereby a sufficient uninterrupted acceleration process, for example detectable by the continuous increase of the operating speed rpm from the time t ₁ to the time t ₂ (ie a corresponding operating speed change Δrpm within a given period .DELTA.t) is ensured.

From the time t ₂ can thus be closed by the sensor assembly 5 to a locked state of the tool 3 on the tool spindle 2. For example In each case, a threshold value _SΔrpm for a rotational speed change Δrpm and / or a threshold value S _rpm for an operating rotational speed rpm of the tool spindle 2 and / or a threshold value S _i for a current consumption i and / or power consumption of the electric machine tool 1 can be used, if this is exceeded, a locked one Condition of the tool 3 is determined on the tool spindle 2.

Alternatively to the in FIG. 3 illustrated and described method for determining the Arretierzustands by monitoring the startup process, an operation of the power tool 1 can be monitored by the sensor assembly 5. An operating procedure can be concluded, for example, when the current consumption i of the electric machine tool 1 exceeds a defined threshold value S _i and likewise the operating rpm rpm of the tool spindle 2 exceeds a defined threshold value S _rpm .

It should be mentioned that in principle according to the invention any number of possible locking states, up to a stepless detection of a locking state, can be determined. In the variant shown in the embodiment only two possible locking states are determined, in particular an unlocked state of the tool 3 and a locked state of the tool 3; However, a person skilled in the art is able, on the basis of the exemplary embodiment and the general description, to expand the invention, if necessary, to a larger number of locking states or a stepless determination of locking states.

In FIG. 4 By way of example, two brake ramps 10, 11 are shown, which can result by selecting two maximum braking torques M _B1 , M _B2 . Here is a steep braking ramp 10, ie a braking ramp 10, which leads to a rapid deceleration of the tool 3 and the tool spindle 2 and a flat braking ramp 11, which leads to a slow deceleration represented.

A time-braking torque functions and / or a maximum braking torque can be chosen in particular such that a previous drive torque, with which the tool spindle 2 has been applied, is not exceeded.

Advantageously, each determined locking state is assigned exactly one maximum braking torque M _B1 , M _B2 or a time braking torque function or a braking ramp 10, 11, for example a steep braking ramp 10 or a flat braking ramp 11. For example, based on the monitored operating speed rpm, ie, for example, based on the time operating speed function rpm (t) of FIG. 3 a locked state of the tool 3 detected at the tool spindle 2 at time t ₂ , it can be provided that the brake assembly 4, the tool spindle 2 then decelerates comparatively quickly with the steep braking ramp 10. Before reaching the time t ₂ , the brake assembly 4 would act on the tool spindle 2 only with the flat brake ramp 11. Thus, it is ensured at all times that the tool spindle 2 is braked as quickly as possible without, however, that the tool 3 can loose or loosen uncontrollably from the tool spindle 2.

In place of in FIG. 4 shown linear brake ramps 10, 11 can also arbitrarily complex braking ramps, z. B. based on asymptotically extending curves or other curves, be provided.

Since a variety of possible circuits and combinations in the context of the invention can be realized, for illustrative purposes only an exemplary circuit of the sensor array 5 in FIG. 5 to be discribed.

The FIG. 5 shows the logical links in an exemplary sensor assembly 5 of the power tool 1. It is provided for simplicity that the sensor assembly 5 determines a binary locking state of the tool 3 on the tool spindle 2 (not locked / locked) and the subsequent selection device 9, for example, a multiplexer, a corresponding control signal y for selecting one of two possible time-braking torque functions or maximum braking torques M _B1 , M _B2 and braking ramps 10, 11 transmitted.

In principle, an unratched tool 3 is assumed (logical '0'), except one of two conditions a, b or both conditions a, b are fulfilled (logical disjunction "≥1").

In the present case, the first condition a is an uninterrupted acceleration process of the tool spindle 2 during a startup process of the electric machine tool 1, which, for example, according to FIG FIG. 3 described manner is determined. In particular, it is possible to monitor whether a threshold value S _{Δrpm of} an operating speed change Δrpm is exceeded within a predefined time range Δt.

The second condition b concerns the question of whether the power tool 1 has been operated. In this case, operation of the power tool 1 is concluded when the two conditions b ₁ and b _{2 are} true (logical conjunction "&").

The condition b ₁ is met exactly when the current consumption i of the electric machine tool 1 exceeds a defined threshold value S _i . The condition b ₂ is met when the operating speed rpm of the tool spindle 2 exceeds the defined threshold value S _rpm .

bzw. in alternativer Schreibweise: $$\mathrm{y}=\mathrm{a}\vee \mathrm{b}=\mathrm{a}\vee \left(\mathrm{b}\mathrm{1}\wedge \mathrm{b}\mathrm{2}\right),$$

mit a='1' für einen vorgegebenen unterbrechungsfreien Beschleunigungsvorgang (sonst a='0'), b='1' im Falle einer betriebenen Elektrowerkzeugmaschine 1 (sonst b='0'), b₁='1' falls i > S_i (sonst b₁='0') und b₂='1' falls rpm > S_rpm (sonst b₂='0').A Boolean function for determining the binary locking state ('0' = unlocked, '1' = locked) and generation of the control signal y can be described according to this example as: $$\mathrm{y}=\mathrm{a}+\mathrm{b}=\mathrm{a}+{\mathrm{b}}_{\mathrm{1}}{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="imgf0001.png"\; state="\{\{state\}\}">b</figure-callout>}}_{\mathrm{2}}$$

or in alternative notation: $$\mathrm{y}=\mathrm{a}\vee \mathrm{b}=\mathrm{a}\vee \left(\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}\mathrm{1}\wedge \mathrm{<figure-callout\; id="2"\; label="b"\; filenames="imgf0001.png"\; state="\{\{state\}\}">b</figure-callout>}\mathrm{2}\right).$$

with a = '1' for a given uninterrupted acceleration process (otherwise a = '0'), b = '1' in the case of a powered power tool 1 (otherwise b = '0'), b ₁ = '1' if i> S _i (otherwise b ₁ = '0') and b ₂ = '1' if rpm> S _rpm (otherwise b ₂ = '0').

Preferably, a computer program with program code means is provided to carry out the described method. The program can then be executed on a microprocessor of a computer, in particular on an electronic control and / or control unit 12 of the power tool 1. For example, the sensor arrangement 5 and / or the selection circuit 9 can be arranged in such a control and / or control unit 12, as shown in FIG FIG. 2 is shown in dashed lines.

Claims (15)

Method for braking a tool spindle (2) of a power tool (1), comprising the following steps: - Determining a locking state of a tool (3) on the tool spindle (2) by a sensor arrangement (5); Selecting a time braking torque function and / or a maximum braking torque (M _B1 , M _B2 ) on the basis of the determined locking state; and - Braking the tool spindle (2) by a brake assembly (4) according to the selected time-braking torque function and / or such that the selected maximum braking torque (M _B1 , M _B2 ) is not exceeded. The method of claim 1, wherein a tool-free locking of the tool (3) on the tool spindle (2), in particular a self-locking when driving or accelerating the tool (3), is provided. The method of claim 1 or 2, wherein the sensor assembly (5) the locking state by monitoring a locking force of the tool (3) on the tool spindle (2), an imbalance of the driven or braked tool (3), achieved before deceleration operating speed (rpm ) of the tool spindle (2), an angular acceleration of the tool spindle (2) achieved before deceleration, and / or a power consumption (i) and / or power consumption of the power tool (1) achieved before deceleration. Method according to one of claims 1 to 3, according to which one of at least two possible locking states is determined, preferably an unlocked state of the tool (3) on the tool spindle (2) and a locked state of the tool (3) on the tool spindle (2). , Method according to one of Claims 1 to 4, according to which the sensor arrangement (5) monitors a starting process of the power tool (1) and determines a locked state of the tool (3) on the tool spindle (2) if during the starting process at least one predetermined uninterrupted acceleration process of Tool spindle (2) has taken place. Method according to one of Claims 1 to 5, according to which a threshold value (S _Δrpm ) for a speed change (Δrpm) of the tool spindle (2) and / or a threshold value (S _i ) for current consumption (i) and / or power consumption of the power tool (1 ) is used, or in whose exceeding a locked state of the tool (3) on the tool spindle (2) is determined. Method according to one of claims 1 to 6, according to which the sensor arrangement (5) monitors an operating process of the power tool (1) and determines a locked state of the tool (3) on the tool spindle (2) when the power tool (1) has been operated. Method according to one of claims 1 to 7, wherein the braking torque (M _B1 , M _B2 ), which is introduced via the brake assembly (4) on the tool spindle (2) is selected such that a previous drive torque with which the tool spindle ( 2) was applied, is not exceeded. Method according to one of claims 1 to 8, according to which each detectable locking state is or are assigned exactly one maximum braking torque (M _B1 , M _B2 ) and / or exactly one time braking torque function. Method according to one of claims 1 to 9, wherein a first maximum braking torque (M _B1 ) for braking the tool spindle (2) is used when a locked state of the tool (3) has been determined on the tool spindle (2) and a second maximum braking torque (M _B2 ) is used to decelerate the tool spindle (2) when an unlocked state of the tool (3) has been determined on the tool spindle (2), wherein the first maximum braking torque (M _B1 ) is greater than the second maximum braking torque ( M _B2 ). Electric power tool (1) comprising a tool spindle (2) on which a tool (3) can be locked, further comprising an electric drive arrangement (M) for driving the tool spindle (2) and a brake arrangement (4) for braking the tool spindle (2) and a sensor arrangement (5) for determining a locking state of the tool (3) on the tool spindle (2), wherein the sensor arrangement (5) and the brake arrangement (4) are designed to carry out a method according to one of claims 1 to 10. Electric power tool (1) according to claim 11, wherein a tool-free locking of the tool (3) on the tool spindle (2), in particular a self-locking when driving or accelerating the tool (3), is provided. Electric machine tool (1) according to claim 11 or 12, wherein the electric drive assembly (M), in particular a DC motor or a single-phase series motor, as part of the brake assembly (4) is used to introduce a braking torque (M _B1 , M _B2 ). Electric machine tool (1) according to one of claims 11 to 13, wherein the power tool (1) is designed as an angle grinder and / or the tool (3) as a grinding wheel or are. Computer program with program code means for carrying out a method according to one of Claims 1 to 10, when the program is stored on a microprocessor of a computer, in particular on an electronic control and / or regulating device (12) of a power tool (1) according to one of Claims 11 to 14, is executed.

Images