Method for operating a machine tool, and machine tool

Abstract

A method for operating a machine tool, in particular an angle grinder, comprising a tool rotatably bringable into operative connection with a driven shaft, the machine tool having a drive device for actuating the driven shaft, a control device for actuating the drive device and at least one sensor device operatively connected to the control device. The method has the following steps: determining a speed value of the driven shaft; determining a speed value of the tool using the sensor device, which interacts with the tool, controlling an output device and/or controlling, in a predefined manner, the drive device via the control device when a difference between the determined speed value of the driven shaft and the determined speed value of the tool is greater than a defined limit value. A machine tool for carrying out a method of this kind is also described.

Claims

1-6. (canceled)

7. A method for operating a machine tool having a tool rotatably bringable into operative connection with a driven shaft, wherein the machine tool has a drive for actuating the driven shaft, a controller for actuating the drive and at least one sensor operatively connected to the controller, the method comprising the steps of: determining a speed value of the driven shaft; determining a speed value of the tool using the sensor interacting with the tool; and controlling an output device or controlling, in a predefined manner, the drive via the controller when a difference between the determined speed value of the driven shaft and the determined speed value of the tool is greater than a defined limit value.

8. The method as recited in claim 7 wherein the speed value of the driven shaft is determined by evaluating a motor current or via an angle sensor interacting with the driven shaft.

9. The method as recited in claim 7 wherein the sensor determines the speed of the tool is an optical, magnetic or electrostatic sensor.

10. The method as recited in claim 7 wherein the output device is controlled, the output device designed to output an acoustic or optical or haptic signal.

11. The method as recited in claim 7 wherein the controlling the drive in the predefined manner includes the controller switching off the drive when the defined limit value is exceeded.

12. The method as recited in claim 7 wherein the machine tool is an angle grinder.

13. A machine tool for carrying out the method as recited in claim 7, a tool rotatably bringable into operative connection with the driven shaft, the machine tool comprising the drive for actuating the driven shaft, the controller for actuating the drive device and the at least one sensor interacting with the control device.

14. The machine tool as recited in claim 13 wherein the machine tool is an angle grinder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In the drawings:

[0021] FIG. 1 is a greatly simplified side view of a hand-held machine tool designed as an angle grinder, a tool designed as a cutting disk being arranged on a driven shaft of the angle grinder; and

[0022] FIG. 2 is a flow chart of an embodiment of a method according to the invention.

DETAILED DESCRIPTION

[0023] FIG. 1 shows a machine tool or hand-held machine tool 1 according to the invention, which is designed as an angle grinder in the illustration shown. According to an alternative embodiment, the machine tool 1 can also be designed as a drilling machine, as a sawing machine, for example a circular saw, or the like.

[0024] The machine tool 1, which is designed as an angle grinder in the drawings, has a housing 2 and a tool 3, which is, for example, designed as a cutting disk. The housing 2 preferably has at least one holding region at which a user can hold and guide the machine tool 1 using one or both hands. The tool 3 can be actuated by a drive, which is in particular designed as an electric motor, or a drive device 4, which can be supplied with current in particular by means of an accumulator 5 that can be connected to the hand-held machine tool 1. According to an alternative embodiment (not shown in the drawings), the hand-held machine tool 1 can also be supplied with electrical current from a network by means of a power cable.

[0025] The drive 4 for actuating the tool 3 in a rotating movement is arranged in the interior of the housing 2 along with a transmission 6 and a driven shaft 7. The drive 4, which is designed, for example, as an electric motor, the transmission 6 and the driven shaft 7 are arranged in the housing 2 relative to one another and are interconnected in such a way that a torque generated by the electric motor 4 can be transmitted to the transmission 6 and finally to the driven shaft 7. A freely rotating end of the driven shaft 7 that projects downward from the housing 2 is connected to the tool, which is designed here as a cutting disk 3, for example via a clamping device (not shown in more detail). The torque of the driven shaft 7 can thus be transmitted to the cutting disk 3.

[0026] The hand-held machine tool 1 also has a control device 8 and, in the present case, two sensor devices 9 and 10. The sensor devices 9 and 10 are electrically and electronically connected to the control device 8. Signals can be sent between the sensor devices 9 and 10 and the control device 8. The control device 8 is in turn electrically and electronically connected to the electric motor 4 and the accumulator 5. Signals can be sent between the sensor devices 9 and 10 and the electric motor 4 and the accumulator 5. The control device 8 is used, inter alia, for controlling and regulating the drive 4 and for supplying power to the hand-held machine tool 1.

[0027] In the present case, the first sensor device 9 is designed to determine a speed of the driven shaft 7 and is designed, for example, as an angle sensor. The speed values of the driven shaft 7 that are determined by the first sensor device 9 are transmitted from the first sensor device 9 to the control device 8. Alternatively, it is also possible for speed values of the driven shaft 7 to be determined by evaluating a motor current of the electric motor 4.

[0028] The second sensor device 10 is designed in the present case as an optical sensor device and directly determines a speed of the tool 3 by interacting with a surface of the tool 3 that varies in the circumferential direction of the tool 3. Optical markings of the tool 3 are used, for example, to determine the speed of the tool 3. The speed values of the tool 3 that are determined by the second sensor device 10 are transmitted from the second sensor device 10 to the control device 8.

[0029] As an alternative to the embodiment as an optical sensor device, the second sensor device can also determine a speed of the tool 3 by interaction with the tool 3 on the basis of a magnetic, electrostatic or other physical operating principle. The speed of the tool 3 can also be determined on the basis of a magnetic resistance (reluctance) or an electrical resistance.

[0030] FIG. 2 shows, in a simplified manner, the sequence of an embodiment of a method according to the invention, by means of which method injury to a user and damage to the machine tool 1, for example due to a tool 3 becoming detached from the driven shaft 7, can be prevented in a simple and reliable manner.

[0031] The method begins at the start S, in particular when the electric motor 4 is actuated. In a first step S1, speed values of the driven shaft 7 are determined by means of the first sensor device 9 and said values are transmitted to the control device 8. In a second step S2, which is carried out in particular at the same time as the first step S1, speed values of the tool 3 are determined by means of the second sensor device 10 and said values are transmitted to the control device 8.

[0032] The control device 8 compares, in step S3, the speed values determined in particular simultaneously by the sensor devices 9, 10, by subtracting in particular the respective speed values of the tool 3 that are determined at a specific point in time by the second sensor device 10 from the speed value of the driven shaft 7 that is determined at the substantially identical point in time by the first sensor device 9.

[0033] In step S4, the control device 8 compares the determined difference with a predefined limit value, which is in particular equal to zero or preferably has a small value, and checks whether the difference is greater than the predefined limit value.

[0034] If the query result is negative, the method is continued with step S1.

[0035] If the query result from step S4 is positive, which can be attributed, for example, to detachment of the tool 3 from the driven shaft 7, i.e. if the difference is greater than the predefined limit value, the control device 8 controls the electric motor 4 in step S5 such that the electric motor 4 is actively braked and the driven shaft 7 quickly comes to a standstill. In this way, injury to a user and damage to the machine tool 1 caused by a tool 3 becoming detached can be prevented in a simple and reliable manner. In addition to the active braking of the electric motor 4, for this purpose the user can alternatively or additionally be given acoustic, optical or haptic feedback via an output device in the event that the predefined limit value is exceeded.

[0036] In step E, the method is ended in particular when the electric motor 3 is no longer operated by the user.