APPLICATION-OPTIMIZED DEACTIVATION BEHAVIOR OF AN ELECTRONIC SLIPPING CLUTCH

Abstract

A method for operating a clutch in a power tool having an electric motor having an open-loop and closed-loop control device for closed-loop and open-loop control of motor power of the tool, and having a sensor, wherein the tool is operable in a first or second operating mode; in the first mode, the clutch is actuated after a predetermined time if a predetermined rotational speed threshold is undershot, and in the second mode, the clutch is actuated if a first predetermined motor current threshold value is exceeded. The method comprises setting the second mode; measuring the current of the motor; and reducing the motor rotational speed from a first rotational speed value to a second rotational speed value if a second predetermined current threshold value is exceeded, wherein a torque that can be generated by the tool is increased from a first torque value to a second torque value.

Claims

1. A method for operating a clutch in a power tool comprising an electric motor; an open-loop control device and a closed-loop control device for closed-loop and open-loop control of motor power of the power tool; and at least one sensor; wherein the power tool is operable in a first operating mode ora second operating mode and, in the first operating mode, the clutch is actuated after a predetermined duration if a speed of the motor falls below a predetermined speed threshold value and, in the second operating mode, the clutch is actuated if a first predetermined motor current threshold value is exceeded, the method including setting the second operating mode; measuring motor current of the electric motor; and reducing the motor speed from a first speed value to a second speed value if a second predetermined motor current threshold value is exceeded, wherein a torque which can be generated by the power tool is elevated from a first torque value to a second torque value.

2. The method as claimed in claim 1, the method including acquiring a first position value and a second position value and a first alignment value and a second alignment value for the power tool by the at least one sensor; and reducing the motor speed from a first speed value to a second speed value if a difference between the first position value and the second position value or a difference between the first alignment value and the second alignment value falls below a predetermined threshold value.

3. The method as claimed in claim 1, the method including setting an activation switch of the power tool into an activation mode; setting the activation switch into a deactivation mode; setting an activation switch into the activation mode; acquiring a first position value and a second position value and a first alignment value and a second alignment value for the power tool by the at least one sensor; and reducing the motor speed from a first speed value to a second speed value if a difference between the first position value and the second position value or a difference between the first alignment value and the second alignment value falls below a predetermined threshold value, wherein the second speed value corresponds to pulsed operation of the electric motor.

4. A power tool operable using the method as claimed in claim 1.

5. The power tool as claimed in claim 4, wherein a transmission comprising at least one first gear and one second gear is provided, wherein in the one first gear, the torque which can be generated by the power tool is in a logarithmic ratio to a motor current increase and, in another gear, the torque which can be generated by the power tool is in a linear ratio to a motor current increase.

6. A power tool operable using the method as claimed in claim 2.

7. A power tool operable using the method as claimed in claim 3.

8. The power tool as claimed in claim 6, wherein a transmission comprising at least one first gear and one second gear is provided, wherein in the one first gear, the torque which can be generated by the power tool is in a logarithmic ratio to a motor current increase and, in another gear, the torque which can be generated by the power tool is in a linear ratio to a motor current increase.

9. The power tool as claimed in claim 7, wherein a transmission comprising at least one first gear and one second gear is provided, wherein in the one first gear, the torque which can be generated by the power tool is in a logarithmic ratio to a motor current increase and, in another gear, the torque which can be generated by the power tool is in a linear ratio to a motor current increase.

Description

[0032] Identical and equivalent components are identified by identical reference signs in the figures. In the figures:

[0033] FIG. 1 shows a schematic illustration of a power tool according to the invention for carrying out the method according to the invention.

EXEMPLARY EMBODIMENT

[0034] FIG. 1 shows a power tool 1 according to the invention for operating the method according to the invention.

[0035] The power tool 1 is embodied in the form of an electric screwdriver or screwdriver drill and substantially contains a housing 2, an electric motor 3 as the drive, a transmission 4 comprising a clutch 5, a driveshaft 6, an output shaft 7, an open-loop and closed-loop control device 8, an activation switch 9, and a rechargeable battery 10.

[0036] The electric motor 3, the transmission 4, the driveshaft 6, and the output shaft 7 are positioned in the housing 2. A first end of a handle 11 for holding the power tool 1 is arranged on the lower side of the housing 2. The activation switch 9 of the power tool 1 is located on the handle 11. The rechargeable battery 10 is detachably attached as an energy source for the power tool 1 at a second end of the handle 11.

[0037] The open-loop and closed-loop control device 8 open-loop controls and closed-loop controls, inter alia, the electric motor 3. For this purpose, the open-loop and closed-loop control device 8 is connected to the activation switch 9, the rechargeable battery 10, and also to the electric motor 3. In particular, the motor current, the speed, and the generated torque can be measured, open-loop controlled, and closed-loop controlled using the open-loop and closed-loop control device 8. The measurement takes place in this case with the aid of sensors (not shown in the figures).

[0038] Furthermore, the power tool contains sensors 12, which can measure various parameters of the power tool and transmit them to the open-loop and closed-loop control device 8. The sensors 12 are gyroscopic sensors and/or acceleration sensors and linear sensors and/or position sensors. The sensors 12 are used to determine a position change and/or alignment change of the power tool 1.

[0039] The electric motor 3 generates a torque and transmits it to the driveshaft 6. The driveshaft 6 is in turn connected to the transmission 4. The transmission 4 contains the clutch 5, which can be embodied in the form of a slipping clutch. A first gear or a second gear can be selected and set in the transmission 4. The output shaft 7 is connected to the transmission 4. The clutch 5 connects or disconnects the driveshaft 6 to or from, respectively, the output shaft 7. A bit 13 (the bit can also be referred to as a screwdriver blade) is fastened on the free end 7a of the output shaft 7. The bit 13 can be inserted into a screw head profile 14a, 15a of a screw 14, 15 (for example, flathead, Phillips, or the like).

[0040] A torque is generated with the aid of the electric motor 3. The generated torque is transmitted to the driveshaft 6, the transmission 4, the clutch 5, the output shaft 7, and finally to the bit 13. If the bit 13 is inserted into the screw head profile 14a, 15a of the screw 14, 15, the torque generated by the electric motor 3 is transmitted to the screw 14, 15 and the screw 14, 15 is rotated in a rotational direction R about a center axis N. Due to the torque acting on the screw 14, 15, the screw 14, 15 can penetrate into the material W and be fastened therein.

[0041] The activation of the clutch 5 is dependent on the measured motor current. The motor current is a function in this case of the torque generated by the electric motor 3. The torque generated by the electric motor 3 can thus be determined by the detection of the motor current. If the measured motor current exceeds a predetermined value, the clutch 5 is activated, i.e., the driveshaft 6 and the output shaft 7 are disconnected from one another. The power tool 1 is designed in this case such that in the first gear, the torque generated by the power tool 1 is in a logarithmic ratio to a motor current increase and in a second gear, the torque which can be generated by the power tool 1 is in a linear ratio to a motor current increase. In this way, a higher torque can be generated in the first gear than in the second gear at identical motor current, without the clutch 5 disconnecting the driveshaft 6 and the output shaft 7.

[0042] If a screw 14, 15 is to be screwed into a material W, a gear for the transmission 4 is firstly selected with the aid of a selection switch 16. A first or a second gear can be selected in this case. However, it is also possible in an alternative embodiment that more than two gears are selectable.

[0043] Subsequently, the corresponding operating mode is selected. It is possible to select between the first operating mode for a soft screw case and the second operating mode for a hard screw case. In the present case, the second operating mode is selected, wherein in the second operating mode, the actuation of the clutch 5 takes place if a first predetermined motor current threshold value is exceeded.

[0044] The selection of the first or second operating mode takes place by means of a selection switch. The selection switch is not shown in the figures.

[0045] Next, the triggering condition of the clutch 5 is set with the aid of a setting device 17. It is determined by this setting from which torque, which is generated by the electric motor 3 and transmitted to the screw 14, 15, the clutch 5 is to disconnect the driveshaft 6 and the output shaft 7. As described above, the torque is determined on the basis of the motor current.

[0046] A first screw 14 is screwed with the aid of the bit 13 into the material W. The activation of the power tool 1 or the electric motor 3 takes place by actuating (pressing) the activation switch 9. The activation switch 9 is moved for this purpose in the arrow direction A. In order to switch off the power 1 or stop the electric motor 3, the activation switch 9 is moved in the arrow direction B. The movement in the arrow direction B is carried out by a spring (not shown). The corresponding sensors continuously measure the motor current in this case. If the torque derived from the motor current does not exceed a previously established threshold value, the screw 14 is screwed into the material W in the direction C up to the stop. The highest torque is generally necessary for the flush countersinking of the screw head 14a, since it generates the greatest resistance in the material W due to its truncated cone shape.

[0047] After the first screw 14 has been screwed into the material W, a second screw 15 is screwed into the material W at another point. It is possible in this case that the second screw 15 is to be screwed in at a point at which the material W is harder than at the point of the first screw 14. In this case, a higher torque is necessary for the screwing in. If the threshold value for the motor current, using which the generated torque can be determined, is exceeded during the screwing in of second screw 15 at a hard point of the material W, the clutch 5 is not activated and thus does not disconnect the driveshaft 6 and the output shaft 7. Instead, the speed of the electric motor is reduced, and therefore the torque can be increased accordingly. The second screw 15 and in particular the screw head 15a can be screwed flush even into a hard material W by the elevated torque. The user of the power tool 1 does not have to release the activation switch 9 in this case (in the arrow direction B), but rather can keep it pressed (in the arrow direction A), since the reduction of the speed and thus the elevation of the torque take place automatically. Due to the low speed and the slow penetration of the screw 14, 15 into the material W linked thereto, it is moreover easier for the user to observe when the screw 14, 15 or the screw head 14a, 15a presses flush against the surface of the material W. Excessively deep penetration of the screw 14, 15 into the material W can thus be prevented.

[0048] An alternative embodiment of the present invention will be described hereafter. In the case in which an excessively high torque is required for the screwing in and this is determinable on the basis of a motor torque lying above a threshold value, the electric motor 3 is completely stopped. The user thereupon releases the activation switch 9 (in the arrow direction B) and subsequently actuates it again (in the arrow direction A). The sensors 12, i.e., the gyroscopic sensors and/or acceleration sensors and the linear sensors and/or position sensors, do not determine a position or alignment change of the power tool 1, however. This means that the power tool 1 was not moved away from the screw 14, 15, and the same screw 14, 15 is still supposed to be screwed. In this way, it is indicated to the open-loop and closed-loop control device 8 that the electric motor 3 is supposed to rotate at a low speed and accordingly generate high torque. Alternatively, the electric motor 3 can also be operated with pulsed operation instead of at a reduced speed. In pulsed operation, the output shaft 7 only rotates in quarter rotations about the center axis N. The torque is also elevated in this way and the screwing in of the screw 14, 15 and also the flush countersinking of the screw head 14a, 15a can be continued.

[0049] However, if the sensors 12, i.e., the gyroscopic sensors and/or acceleration sensors and the linear sensors and/or position sensors, determine a position or alignment change of the power tool 1 (i.e., on the basis of exceeding of a threshold value and/or falling below a difference value of a first and second position or alignment value), it can be presumed that the power tool 1 was moved from one screw 14 to another screw 15. Therefore, screwing is no longer performed on the same screw 14. In such a case, if the user releases the activation switch 9 (in the arrow direction B) and subsequently actuates it again (in the arrow direction A), the speed of the electric motor 3 is not reduced and pulsed operation is also not set. The new screw 15 can now be screwed again using the full speed range.