EP3393710B1 - Method for operating a power tool - Google Patents

Description

The invention relates to a method for operating an electric tool according to claim 1, a control device for executing the method according to claim 11 and an electric tool according to claim 12.

State of the art

In the prior art, for example, battery-operated electric screwdrivers are known, which are used to tighten or loosen a screw. When loosening a screw, it can be advantageous to automatically stop turning the power tool, as in US 2003 014 9508 A1 and DE 10 2009 002 858 A1 is described.

Disclosure of the invention

The object of the invention is to provide an improved method for loosening a screw element with the aid of a power tool.

The object of the invention is achieved with the help of the independent claims. Further advantageous embodiments are specified in the dependent claims.

An advantage of the method described is that a connection to the screw element and the positive and / or non-positive connection of the screw element with a counterpart is taken into account when loosening. This enables a better adaptation of the performance to the current situation. These advantages are achieved through the proposed method for operating an electric tool with an electric motor for loosening a screw element from a counterpart, wherein in a second section a time profile of the power is recorded for a predetermined second time period, with a change being made to a third area if the power during the second time period exceeds a second power limit and a temporal fluctuation of the power lies within a predetermined fluctuation value, a third power limit being determined as a function of the detected power in the second section, with a switch from the third section to a fourth section if the power within a predetermined third time period falls below the third performance limit,
in the fourth section, the power of the electric motor is reduced by at least 30%. By determining the third performance limit depending on the performance in the second section, an improved loosening of the screwing element is achieved, the load on the screwing element being reduced and energy being saved when loosening the screwing element. This is particularly advantageous for power tools that are powered by a battery.

In one embodiment, at least two, in particular five, measurements of the power consumed by the electric motor are carried out in the second section, with a switch being made to the third section when the measured powers are within the predetermined fluctuation value. This enables a more precise detection of the existing connecting force between the screw element and the counterpart.

In one embodiment, the measurements of the power are each carried out for a predetermined period of time, in particular for at least 8 milliseconds, the measured powers being averaged, with a change being made to the third section when the averaged powers are within the predetermined fluctuation value. This enables a more precise determination of the actual connection force.

In one embodiment, the power is measured on the basis of a current that is absorbed by the electric motor. This allows the performance to be estimated using simple means.

In one embodiment, the third power limit is determined from an averaged sum of the powers measured in the second section multiplied by a factor less than 1. In this way, a suitable determination of the third performance limit can be achieved in a simple manner.

In one embodiment, the third performance limit is assigned a predetermined value if the conditions of the second section are not met within a predetermined period of time and then branches to the third section. A function of the method is thus guaranteed.

In one embodiment, in the fourth section, rotation of the rotary element is braked, in particular stopped, after a predetermined number of revolutions has been reached. This avoids a complete loosening of the screw element from the counterpart.

In one embodiment, the power of the electric motor is reduced, in particular the electric motor is switched off when it is determined in the second section that the power consumed by the electric motor is below the second power limit. A load-free case in which no loosening of a screw element is required can thus be recognized and energy can be saved.

In one embodiment, the first performance limit is greater than the second performance limit. Tests have shown that this provides good solving methods.

The proposed power tool has an electric motor for rotating a rotating element, a power supply, a switch for selecting an automatic release function for releasing a screw element from a counterpart.

In one embodiment, a display is provided, the display indicating whether the automatic release function has been activated. This can cause a Operating function monitor the function of the power tool and is not surprised by the automatic function.

In one embodiment, the display is arranged in a lower region of a handle of the power tool. This makes the display easy for the operator to see.

In one embodiment, the display is designed to display at least two rotational speeds of the rotating element.

In one embodiment, the switch and the display are arranged side by side.

• Fig. 1 in einer schematischen Darstellung ein Elektrowerkzeug 1,
• Fig. 2 eine vergrößerte Darstellung einer Anzeige,
• Fig. 3 eine vergrößerte Darstellung einer weiteren Ausführungsform der Anzeige,
• Fig. 4 eine vergrößerte Darstellung einer weiteren Anzeige,
• Fig. 5 eine schematische Darstellung eines Programmablaufes zur Durchführung des Verfahrens.

The invention is explained in more detail below with reference to the figures. Show it:

• Fig. 1 a schematic representation of an electric tool 1,
• Fig. 2 an enlarged representation of an advertisement,
• Fig. 3 an enlarged view of a further embodiment of the display,
• Fig. 4 an enlarged view of another display,
• Fig. 5 is a schematic representation of a program sequence for performing the method.

Fig. 1 shows a schematic representation of an electric tool 1, which has a rotating element 2, which is provided in operative connection with a screw element for rotating the screw element, in particular for loosening the screw element from a counterpart. The power tool has an electric motor 16 which is connected to a power source. The power source can be provided by a rechargeable battery, ie a rechargeable battery or a power supply. In the exemplary embodiment shown, a rechargeable battery 3 is provided, which is arranged, for example, releasably on a lower end of a handle 4 of the power tool 1. At the upper end, the handle 4 merges into a motor housing 5, at the front end of which the rotary element 2 is formed. Depending on the selected direction of rotation, the rotating element 2 is rotated clockwise or counterclockwise by the electric motor. To operate the power tool is on a button 6 is provided at the upper end of the handle 4. When the button 6 is pressed in the direction of the handle 4, the rotating element 2 is rotated. Furthermore, a direction of rotation selector 7 is provided on the upper end region of the handle 4 on a side surface. The direction selector 7 specifies the direction of rotation. Thus, the operator can use the direction of rotation selector 7 to determine whether a screwing element is to be screwed on or unscrewed from the counterpart, that is, to be released. The power tool 1 has a control unit 14, which is provided with sensors 17 for detecting the power that is output by the electric motor. For example, the power of the power tool can be estimated on the basis of the current strength consumed by the electric motor. In addition, the control device 14 is connected to a data memory 15. Furthermore, the control device 14 is designed to influence the functioning of the electric motor 16, in particular to control the power and / or to brake the rotation of the rotary element 2. The electric motor 16 is supplied, for example, with a pulse width modulated voltage which is controlled by the control device.

In the exemplary embodiment shown, a display 8 is provided at the lower end of the handle 4, which indicates to an operator whether a method for automatically loosening the screwing element is active. For this purpose, the display 8 has corresponding optical means for displaying. For example, the display 8 lights up red in particular when the method for automatically loosening the screw element is active.

Fig. 2 shows the display 8 in an enlarged view, the display 8 having a display field 9 which lights up or flashes when the automatic release function is active. In addition to the display field 9, an actuation field 13 is provided, in which a button is provided. By pressing the operating field 13, the button is actuated and the selection of the automatic release method is activated.

Fig. 3 shows a further embodiment of the display 8, in which a speed display in the form of two further fields 10, 11 is provided in addition to the display field 9. The first further display field 10 lights up when the Speed of the power tool is in a first speed range. The second further display field 11 lights up when the speed of the power tool is in a second speed range, the second speed range being greater than the first speed range.

Fig. 4 shows a further embodiment, in which three further display fields 10, 11, 12 are provided for displaying three speed ranges. In this embodiment, the display field 9 has been omitted.

Depending on the selected embodiment, the actuation field 13 can be dispensed with and the automatic release function can be started automatically by a control device of the power tool if predetermined boundary conditions exist.

Fig. 5 shows a schematic representation of a program sequence for operating the power tool. The program is started at program point 100. At program point 110, the control device is initialized or the power tool is operated in normal operation, in which, for example, the speed of rotation of the rotating element 2 is set as a function of the depth of depression of the button 6. At program point 120 it is checked whether the program for the automatic loosening of a screw element is selected and the power tool 1 is in the direction of rotation for loosening a screw element. For example, it is checked whether the operating field 13 has been pressed. Depending on the selected embodiment, the determination as to whether an automatic release process is to be carried out can also be determined by the control unit on the basis of predetermined parameters which are stored in the data memory. For example, the automatic release process can always be activated when the rotating element corresponds to a loosening of a screwing element, ie when turning to the left. If this is not the case, the program branches back to program point 110.

However, if it is recognized at program point 120 that the automatic release function is to be carried out, the program branches to program point 130.

At program point 130, it is checked whether the button 6 is pressed. If this is not the case, the program branches back to program point 110. If the button 6 is not pressed, then no turning of the rotating element is desired. However, if the button 6 is pressed at program point 130, the program branches to program point 140.

At program point 140 it is checked whether the power consumed by the electric motor is above a first power limit. The power consumed is e.g. detected with a sensor 16 or by the control unit 14 on the basis of operating parameters such as an impression depth of the button 6 is estimated. The first power limit can be 20 A, for example. The first power limit can depend on the type of power tool and other general conditions, e.g. are detected by the control device 14 or are stored in the data memory. The first performance limit can be stored in the data memory 15. If it is recognized at program point 140 that the first performance limit has not been exceeded, the program branches to program point 150. At program point 150, it is recognized that the load is too low and the rotation of the electric motor is reduced by control unit 14, in particular the power supply of the electric motor is reduced and, for example, reduced to the value 0. The program then branches back to program point 110.

If it is recognized at program point 140 that the electric motor consumes more than the first power limit, program point 160 detects the presence of a first section. The program then branches to program point 170. At program point 170, a first minimum time is read out of data memory 15. The first minimum time can be predetermined constantly or, depending on the first performance limit or depending on further operating parameters, can be stored in the form of a table and a characteristic curve in the data memory 15. The first minimum time can be, for example, 80 ms.

At program point 180, a first time counter is started and a check is carried out to determine whether the electric motor consumes a power that is above the first power limit for longer than the predetermined first minimum time. Returns the Checking at program point 180 that the electric motor has always consumed more than the first power limit for longer than the first minimum time, then at program point 190 the presence of a second section is recognized. After program item 190, the program branches to program item 200.

At program point 200, a second time counter is started. At program point 210, it is checked whether the second time counter has reached a predetermined second time period. The second time period can be predefined constantly or, depending on the first performance limit or depending on further operating parameters, can be stored in the form of a table and a characteristic curve in the data memory 15. The second period can e.g. 80 ms.

If the program detects at program point 210 that the second time counter has reached the second time period, the program branches to program point 220 and a second performance limit is assigned a value which is stored in data memory 15. The second power limit set at program point 220 can have different values depending on the power tool used and the present operating conditions. For example, the second performance limit can be lower than the first performance limit. Program point 220 is provided to provide a second performance limit in the case of difficult-to-understand boundary conditions.

If the query at program point 210 shows that the second time period has not yet been reached, the program branches to program point 230. At program point 230, several measurements of the power consumed by the electric motor are carried out. For example, five measurements of the performance are carried out in succession. The measurements are carried out in a predetermined time window, for example within 40 ms. In a subsequent program step 240, it is checked whether the measurements carried out meet predetermined conditions. The specified conditions are stored in the data memory. The condition is, for example, that the measured outputs must each be above a predetermined second output limit. The second power limit can be 19 A, for example.

Another condition is e.g. in that the fluctuations in the measured outputs, i.e. the differences in the measured outputs are smaller than a predetermined value. For example, the predetermined value for the fluctuation can be 10% of an average power. The averaged power can be determined by the sum of the averaged measured powers averaged by the number of measurements. This means that the averaged measured power may deviate less than 10% from an averaged value of the measured power to meet this condition. In addition, the value for the fluctuation can be specified as a constant value and e.g. a current of 4 A.

If the specified conditions at program point 240 are not met, the program branches back to program point 210. The second period is so long that, for example, two or more measurement methods and evaluations can be carried out according to program points 230 and 240 before branching to program point 220.

However, if the query at program point 240 reveals that the specified conditions are met by the measured outputs, the program branches to program point 250. At program point 250, a third performance limit is determined based on the measurements of the performance at program point 230. For example, the third power limit is calculated from the averaged value of the measured powers multiplied by a factor less than 1, for example 0.7. Depending on the selected embodiment, other methods and calculation methods can also be used to determine the third power limit on the basis of the measured powers. The program then branches to program point 260.

Likewise, after processing from program point 220, the program branches to program point 260. At program point 260, a third section is recognized. The program then branches to program point 270. At program point 270, the power of the electric motor is recorded. At a subsequent program point 280, it is checked whether the power consumed by the electric motor is less than the third power limit for a predetermined third Duration is. The third time period can be 16 ms, for example, and can be stored in the data memory 15. If the condition of program point 280 is not met, the program branches back to program point 270. However, if the condition of program point 280 is met, the program branches to program point 290 and a fourth section is recognized. After program point 290, the program branches to program point 300. At program point 300, the control unit reduces the power of the electric motor. The performance is reduced by at least 30%. The electric motor can be controlled, for example, with a pulse width modulated signal. The power reduction at program point 300 can also be up to 70%. In addition, the number of revolutions of the rotating element 2 is counted using a further sensor 17, for example using a Hall sensor.

It is then checked at program point 310 whether a predetermined number of revolutions has been reached. If this is not the case, the program branches back to program point 300. However, if it is determined at program point 310 that a predetermined number of revolutions has been carried out in the fourth section, the program branches to program point 320. At program point 320, the power of the electric motor is reduced further, in particular the electric motor is switched off. In addition, the rotating element can also be braked. For this purpose, mechanical means or a corresponding pulse-width-modulated control of the electric motor can be carried out. The end of the automatic release process is then determined at program point 330 and branched back to program point 110.

The predetermined number of revolutions, after which the change from program point 310 to program point 320 can be, for example, the number 4. Depending on the embodiment chosen, however, other, i.e. smaller or larger numbers of rotations may be provided before changing to program point 320.

Depending on the selected embodiment, the power can also be estimated or measured by other means than by measuring the absorbed current.

The first area is used to detect the presence of a load when the automatic release function is present.

In the second area, an existing fastening situation is recorded and a limit value for the second performance limit is determined depending on it. Depending on the selected embodiment, the averaged value at program point 250 can also be multiplied by a factor of 0.5 or 0.8.

The third area is provided to detect the presence of a loosened screw element.

The fourth area is provided in order to carry out a further loosening of the screw after the detection of a loosened screw, without preferably loosening the screw completely from the counterpart, in particular a screw bolt.

With the aid of the proposed method, an improved loosening of a screw element is achieved, in particular a complete loosening of the screw element from a counterpart, in particular a bolt, is to be avoided. The screw element can be designed as a screw, bolt or in another form.

Claims (15)

1. Method for operating an electric power tool having an electric motor for unscrewing a screw element from a mating piece, wherein the electric power tool having a rotary element is operatively connected to the screw element,
   characterized in that in a first mode a check is performed as to whether the power of the electric motor exceeds a predetermined first power limit for a predetermined first minimum period of time,
   wherein after exceeding the first power limit for the first minimum period of time a second mode is adopted,
   wherein a progression with respect to time of the power is ascertained in the second mode for a predetermined second period of time,
   wherein a third mode is adopted if the power during the second period of time exceeds a second power limit and the power fluctuates with respect to time within a predetermined fluctuation value range,
   wherein in dependence upon the ascertained power in the second mode a third power limit is determined,
   wherein a change occurs from the third mode into a fourth mode if the power drops below the third power limit within a predetermined third period of time,
   wherein in the fourth mode the power of the electric motor is reduced by at least 30%.
2. Method according to Claim 1, wherein in the second mode at least two, in particular five, measurements of the power being consumed by the electric motor are performed, wherein the third mode is adopted if the measured powers lie within the predetermined fluctuation value range.
3. Method according to Claim 2, wherein the measurements of the power are performed in each case for a predetermined period of time, in particular for at least 8 milliseconds, wherein the measured powers are averaged, wherein the third mode is adopted if the averaged powers lie within the predetermined fluctuation value range.
4. Method according to Claim 2 or 3, wherein the power is measured with reference to a current that is drawn by the electric motor.
5. Method according to any one of the preceding claims, wherein the third power limit is determined from an averaged sum of the powers that are measured in the second mode multiplied by a factor smaller than 1.
6. Method according to any one of the preceding claims, wherein the third power limit is assigned a predetermined value if the conditions of the second mode are not fulfilled within a predetermined period of time, and wherein subsequently the third mode is adopted.
7. Method according to any one of the preceding claims, wherein in the fourth mode and after a predetermined number of rotations of the rotary element, the power is further reduced by at least 50%.
8. Method according to any one of the preceding claims, wherein in the fourth mode a rotation of the rotary element is braked, in particular stopped, after achieving a predetermined number of rotations.
9. Method according to any one of the preceding claims, wherein the power of the electric motor is reduced, in particular the electric motor is switched off, if in the second mode it is determined that the power being consumed by the electric motor lies below the second power limit.
10. Method according to any one of the preceding claims, wherein the first power limit is greater than the second power limit.
11. Control device (14) that is embodied in order to perform a method in accordance with the preceding claims.
12. Electric power tool (1) having an electric motor (16) for rotating a rotary element (2), having a current supply (3), having a switch (13) for selecting an automatic unscrewing function for unscrewing a screw element from a mating piece in accordance with a method according to any one of Claims 1 to 10.
13. Electric power tool according to Claim 12, wherein a display (8) is provided, wherein the display (8) is embodied in order to display an activated automatic unscrewing function.
14. Electric power tool according to Claim 13, wherein the display (8) is arranged in a lower region of a hand grip (4) of the electric power tool (1).
15. Electric power tool according to any one of Claims 13 or 14, wherein the display (8) is embodied in order to display at least two rotational speeds of the rotary element (2), wherein in particular the switch (13) and the display (8) are arranged adjacent to one another.

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