METHOD FOR OPERATING A MACHINE TOOL AND MACHINE TOOL

Abstract

A method for operating a machine tool having a battery and an electric motor which is designed to rotationally drive an output shaft that can be coupled to a tool, is described, a control device for actuating the electric motor and a device for determining a parameter being provided. The machine tool can be operated in a first operating mode and a second operating mode, the machine tool being transferred from the first operating mode into the second operating mode if the parameter determined by the device exceeds or falls below a defined threshold value. In the second operating mode, the electric motor is controlled by an amperage profile, the amperage profile comprising first current pulses (10) and second current pulses (11). The level of a maximum amperage (A1) of the first current pulses (10) is greater than the level of a maximum amperage (A2) of the second current pulses (11). A machine tool that can be operated using a method of this kind is also described.

Claims

1-14. (canceled)

15. A method for operating a machine tool having a battery, an electric motor designed to rotationally drive an output shaft couplable to a tool, a controller for actuating the electric motor and a determinator for determining a parameter, the machine tool operable in a first operating mode and a second operating mode, and the machine tool being transferred from the first operating mode into the second operating mode if the parameter exceeds or falls below a defined threshold value, the method comprising: controlling the electric motor in the second operating mode by an amperage profile, the amperage profile including at least one first current pulse and at least one second current pulse, a maximum amperage of the first current pulse being greater than a maximum amperage of the second pulse.

16. The method as recited in claim 15 wherein the electric motor is controlled in the second operating mode alternately by a defined number of first current pulses and a defined number of second current pulses.

17. The method as recited in claim 15 wherein the electric motor is controlled in the second operating mode alternately by a first current pulse and then a plurality of second current pulses.

18. The method as recited in claim 17 wherein a number of the plurality of second current pulses is two to twenty.

19. The method as recited in claim 18 wherein a number of the plurality of second current pulses is five to fourteen.

20. The method as recited in claim 19 wherein a number of the plurality of second current pulses is eight to ten.

21. The method as recited in claim 15 wherein the electric motor is controlled in the second operating mode such that a length of the first current pulses differs from a length of the second current pulses.

22. The method as recited in claim 21 wherein the first current pulses are longer than the second current pulses.

23. The method as recited in claim 22 wherein the first current pulses are twice as long as the second current pulses.

24. The method as recited in claim 15 wherein the electric motor is controlled in the second operating mode such that the maximum amperage of the first current pulses is between 25% and 80% larger than the maximum amperage of the second current pulses.

25. The method as recited in claim 24 wherein the electric motor is controlled in the second operating mode such that the maximum amperage of the first current pulses is 50% larger than the maximum amperage of the second current pulses.

26. The method as recited in claim 15 wherein the electric motor controlled in the second operating mode such that the maximum amperage of the first current pulse or a maximum amperage of the second current pulse varies depending on the actual charge status of the battery.

27. The method as recited in claim 15 wherein the maximum amperage of the first current pulse or the maximum amperage of the second current pulse is adjusted discretely or continuously depending on the charge status of the battery.

28. The method as recited in claim 15 wherein proceeding from the first operating mode of the machine tool, an amperage substantially equal to the value zero is applied to the electric motor for a defined period of time before a transition into the second operating mode.

29. The method as recited in claim 15 further comprising transferring the machine tool from the second operating mode into the first operating mode when a torque determined by the determinator and applied to the output shaft becomes less than a threshold torque.

30. The method as recited in claim 15 further comprising stopping the electric motor when the machine tool is in the second operating mode for a period of time greater than a predefined threshold value.

31. The method as recited in claim 15 wherein the parameter determined by the determinator is a torque applied to the output shaft, the machine tool being operated in the first operating mode when the determined torque is less than a defined threshold torque, and the machine tool being transferred from the first operating mode into the second operating mode when the determined torque exceeds the defined threshold torque.

32. The method as recited in claim 15 wherein the parameter determined by the determinator is an acceleration value of the output shaft, the machine tool being transferred from the first operating mode into the second operating mode when the determined acceleration exceeds a defined negative acceleration value.

33. The method as recited in claim 15 wherein the parameter determined by the determinator is a speed of the drive shaft, the machine tool being transferred from the first operating mode into the second operating mode if a speed does not reach a defined threshold speed after a specified period of time.

34. A machine tool comprising: a battery; an electric motor designed to rotationally drive an output shaft couplable to a tool; a controller for actuating the electric motor, and a determinator for determining a parameter, the machine tool being operated according to the method as recited in claim 15.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In the drawings:

[0030] FIG. 1 is a greatly simplified representation of a machine tool having a battery, an electric motor and a control device for actuating the electric motor;

[0031] FIG. 2 is a simplified flow diagram of a method for operating the machine tool according to FIG. 1;

[0032] FIG. 3 shows simplified diagrams which represent, over a period of time, a speed of an electric motor and an amperage which acts on the electric motor, the diagrams showing the operation of the machine tool first in a first operating mode, then in a second operating mode and finally in the first mode of operation again;

[0033] FIG. 4 is a simplified view of a portion of an amperage profile to which the electric motor is controlled in the second operating mode by a control device;

[0034] FIG. 5 is a simplified view of a portion of an alternative amperage profile to which the electric motor is controlled by a control device in the second operating mode; and

[0035] FIG. 6 is a simplified view of a relationship between a charge state of a battery of the machine tool and a maximum amperage of a current pulse of an amperage profile.

DETAILED DESCRIPTION

[0036] FIG. 1 is an exemplary flow diagram of an embodiment of a method according to the invention for operating a machine tool 1, in particular a cordless screwdriver, a drilling machine or the like. The machine tool 1 has a battery 2, which is provided in order to supply power to an electric motor 3 of the machine tool 1. The electric motor 3 is designed to rotationally drive an output shaft 4 of the machine tool 1, it being possible for the output shaft 4 to be coupled to a tool 5, for example a bit, a drill or the like. The machine tool 1 also has a control device 6 for actuating the electric motor 3, the control device 6 being designed to actuate the electric motor 3 in a controlled manner on the basis of an amperage. The machine tool 1 also has a device 7 for determining a parameter of the machine tool 1, in particular a torque applied to the output shaft 4 and/or an acceleration value of the output shaft 4. The machine tool 1 is designed so as to not have a mechanical coupling, such that the electric motor 3 is operatively connected directly to the output shaft 4, optionally by means of an interposed gear.

[0037] The machine tool 1 can be operated in a first operating mode and in a second operating mode. This is discussed in more detail below.

[0038] The method begins with the start S. In a first step S1, the machine tool 1 is operated in accordance with a user request in the first operating mode which corresponds, for example, to a normal drilling mode.

[0039] In a second step S2, the device 7 detects a defined operating state in which continued operation in the first operating mode can, for example, damage the electric motor 3, in particular as a result of overheating. In this case, the device 7 detects or determines, for example, an undesirably high braking torque applied to the output shaft 4 of the tool 5 which exceeds a specified threshold value or a threshold torque. This can occur, for example, when drilling a hole at an advanced borehole depth. Alternatively, the defined operating state can be detected by the device 7 in that the determined absolute value of the acceleration of the output shaft 4 is greater than a defined threshold value and the tool 5 thus experiences a defined braking. This can occur, for example, when a tool 5 becomes locked.

[0040] The device 7 can be designed, for example, as an algorithm stored in the control device 6, which determines or calculates or estimates a parameter directly or indirectly from other input values and compares said parameter with a defined threshold value. The parameter can be, for example, the torque applied to the output shaft 4 or an acceleration value of the output shaft 4.

[0041] After a corresponding detection of the defined operating state, the electric motor 3 is braked to a speed n.sub.mot substantially equal to zero by the control device 6 in step S3.

[0042] The control device 6 then transfers the machine tool 1 into the second operating mode in step S4, which has the purpose of releasing the tool 5 and providing haptic feedback to the user which is comparable to a machine tool having a mechanical coupling. The second operating mode is discussed in more detail below.

[0043] After the tool 5 has in particular been released again, i.e. if, for example, the device 7 detects that a torque applied to the output shaft 4 is less than a defined torque value, in step S5 the control device 6 transfers the machine tool 1 back into the first operating mode, and in step S6 it is checked in turn whether a defined operating state as described above occurs again.

[0044] In step E, the method is ended, for example, as requested by the user.

[0045] FIG. 2 shows an exemplary sequence of a drilling process, the curve of the motor speed n.sub.mot being shown in the upper diagram and an actual curve of the amperage A over time being shown in the lower diagram. The amperage curve substantially corresponds to a curve of a torque applied to the output shaft 4.

[0046] The machine tool 1 is operated in a first phase P1 in the first operating mode, the motor speed n.sub.mot substantially constantly assuming an operating value n.sub.mot1 and the amperage A which is required for operating the electric motor 3 being below a threshold value A.sub.threshold. An applied load torque can also be estimated in the control device 6 instead of the amperage A.

[0047] At a point in time t1, the amperage A increases up to the threshold value A.sub.threshold and/or the estimated load torque increases up to a threshold value M.sub.threshold. This is due, for example, to the fact that the tool 5 enters deeper into a surface and/or the tool 5 locks and becomes stuck in a surface. The defined operating state is determined by the control device 6. In order to protect the electric motor 3 from overheating or other damage, the motor speed n.sub.mot is subsequently substantially set to the value zero in a second phase P2 up to the point in time t2.

[0048] In the following third phase P3, the machine tool 1 is transferred from the first operating mode into the second operating mode, in which the control device 6 acts on the electric motor 3 using a predefined amperage profile, a portion of which is shown in FIG. 4.

[0049] The electric motor 3 is controlled by the control device 6 in the second operating mode on the basis of the amperage profile, of which a portion is shown in FIG. 4, or is regulated to this amperage profile. The amperage profile has first current pulses 10 and second current pulses 11, which in the present case are designed as rectangular pulses having a constant maximum amperage in each case. The maximum amperage A1 of the first current pulses 10 is substantially constant for all of the first current pulses 10, the amperage A1 in the present case being approximately 50% larger than a maximum amperage A2 of the second current pulses 11, which in turn are substantially constant for all of the second current pulses 11. The first current pulses 10 extend over a first period of time T1, which in the present case is substantially twice as long as a period of time T2 of the second current pulses 11. A period of time T3 between two successive current pulses 10, 11 in the present case substantially corresponds to the period of time T1 of the first current pulse 10.

[0050] In the amperage profile, nine second current pulses 11 follow a first current pulse 10 in the present case. It has been found that this results in a favorable compromise between desired haptic feedback to the user which is comparable to that of a machine tool having a releasing mechanical coupling, and low power consumption. In particular, the first current pulses 10 apply a torque to the output shaft 4, which is intended to release the tool 5 from the locked situation.

[0051] At a point in time t3 in the diagrams according to FIG. 3, the motor speed n.sub.mot increases up to the point in time t4 in a fourth phase P4, this being due to the locking situation of the tool being removed. Subsequently, the machine tool 1 is returned to the first operating state by the control device 6 in a fifth phase P5 starting from the point in time t4, the motor speed n.sub.mot being returned to the value n.sub.mot1 after an acceleration phase.

[0052] If, alternatively, the operation of the machine tool 1 over a defined period of time does not result in a lockage of the tool 5 being released, the electric motor 3 can be stopped in order to prevent the electric motor 3 from overheating.

[0053] FIG. 5 shows an alternatively designed amperage profile which substantially corresponds to the amperage profile according to FIG. 4, with the difference that a maximum amperage of the first pulses 10 is not constant over time. In the amperage profile according to FIG. 5, the maximum amperage of the first current pulses 10 decreases depending on the charge state of the battery 2, a further first current pulses 10′ having a maximum amperage A1′ smaller than the maximum amperage A1. FIG. 6 shows an example of a dependence of the maximum amperage of the first current pulses 10 on the charge state of the battery 2, the maximum amperage of the first current pulses 10 decreasing in the present case in discrete values as the charge state of the battery 2 decreases. The charge state of the battery 2 is shown in FIG. 5 as a percentage of a maximum charge state of the battery 2.

[0054] Alternatively, the maximum amperage of the first current pulses 10 can also decrease substantially continuously when contemporary or actual information regarding the charge state of the battery 2 is available.

[0055] Alternatively or in addition, the maximum amperage of the second current pulses 11 can also decrease depending on the charge state of the battery 2.

LIST OF REFERENCE SIGNS

[0056] 1 Machine tool [0057] 2 Battery [0058] 3 Electric motor [0059] 4 Output shaft [0060] 5 Tool [0061] 6 Control device [0062] 7 Device [0063] 10, 10′ First current pulse [0064] 11 Second current pulses [0065] A.sub.threshold Threshold value

[0066] A1, A1′, A2 Maximum amperage [0067] n.sub.mot Motor speed [0068] n.sub.mot1 Operating value of the motor speed [0069] E, S, S1-S6 Method step [0070] P1-P4 Phase [0071] T1, T2, T3 Period of time [0072] t1 to t5 Point in time