Safety Braking Device with Two Braking Stages

Abstract

A safety braking device for a machine tool for braking a processing tool driven by means of an electric motor via an output unit, more particularly an output shaft, includes at least one braking device which is provided to halt rotation of the output unit in a braking process. The braking device has at least a first braking stage and a second braking stage. The disclosure further relates to a machine tool having the safety braking device and to a method for operating a safety braking device.

Claims

1. A safety braking apparatus for a machine tool for braking a cutting tool which is driven by means of an electric motor via an output unit, comprising: at least one braking apparatus comprising at least a first braking stage and a second braking stage, the at least one braking apparatus configured to, in a braking operation, brake, or halt a rotation of the output unit.

2. The safety braking apparatus as claimed in claim 1, wherein the first braking stage and the second braking stage are configured to exert different braking effects during the braking operation.

3. The safety braking apparatus as claimed in claim 1, wherein the first braking stage is configured as an electronic braking stage.

4. The safety braking apparatus as claimed in claim 1, wherein the first braking stage is realized via a reversal of the electric motor.

5. The safety braking apparatus as claimed in claim 1, wherein the first braking stage is configured to, in the braking operation, halt the rotation of the output unit within at most 1,000 milliseconds.

6. The safety braking apparatus as claimed in claim 1, wherein the second braking stage is configured as an electronic braking stage.

7. The safety braking apparatus as claimed in claim 1, wherein the second braking stage is configured as a mechanical braking stage having at least one mechanical braking element.

8. The safety braking apparatus as claimed in claim 1, wherein the second braking stage is configured to, in the braking operation, halt the rotation of the output unit within at most 50 milliseconds.

9. The safety braking apparatus as claimed in claim 1, wherein the at least one braking apparatus is configured to, in the braking operation, first apply the first braking stage in response to detecting an approachment of a user to the cutting tool, and to apply the second braking stage in response to detecting a further approachment of the user to the cutting tool or a touching of the cutting tool by a body part of the user.

10. A hand-held machine tool, comprising: an output unit an electric motor configured to drive a cutting tool via the output unit and a safety braking apparatus comprising: at least one braking apparatus comprising at least a first braking stage and a second braking stage, the at least one braking apparatus configured to, in a braking operation, brake or halt a rotation of the output unit.

11. A method for operating a safety braking apparatus having at least one braking apparatus configured to, in a braking operation, brake or halt a rotation of an output unit of a machine tool via which an electric motor of the machine tool drives a cutting tool, the method comprising: in response to detecting an approachment of a user to the cutting tool, braking or halting the rotation of the output unit is braked, in particular halted, at least substantially by via a first braking stage of the at least one braking apparatus and, in response to detecting a further approachment of the user to the cutting tool or a touching of the cutting tool by the user, braking or halting the rotation of the output unit at least substantially via a second braking stage of the braking apparatus.

12. The safety braking apparatus as claimed in claim 1, wherein the output unit includes an output shaft configured to drive the cutting tool.

13. The safety braking apparatus as claimed in claim 5, wherein the first braking stage is configured to, in the braking operation, halt the rotation of the output unit within at most 500 milliseconds.

14. The safety braking apparatus as claimed in claim 5, wherein the first braking stage is configured to, in the braking operation, halt the rotation of the output unit within at most 200 milliseconds.

15. The safety braking apparatus as claimed in claim 8, wherein the second braking stage is configured to, in the braking operation, halt the rotation of the output unit within at most 20 milliseconds.

16. The safety braking apparatus as claimed in claim 8, wherein the second braking stage is configured to, in the braking operation, halt the rotation of the output unit within at most 5 milliseconds.

Description

DRAWINGS

[0018] The invention is explained in greater detail, on the basis of illustrative embodiments represented in the drawings, in the following description. The drawings, the description and the claims contain numerous features in combination. The person skilled in the art will expediently consider the features also in isolation and put them together to form sensible further combinations. Same reference symbols in the figures denote same elements.

[0019] FIG. 1: shows a machine tool according to the invention in perspective representation,

[0020] FIG. 2: shows a sectional representation through parts of the machine tool, together with safety apparatus and braking apparatus according to the invention, in schematic representation.

[0021] FIG. 3: shows a flow chart of an exemplary braking operation.

[0022] FIG. 1 shows a machine tool 10 according to the invention, realized as a hand-held circular saw 10a. It should be pointed out that the comments should not be deemed to be limited to a hand-held circular saw 10a, but rather the technical teachings on which the comments are based are in principle also transferable to any other machine tools which appear sensible to a person skilled in the art, in particular, for instance, drills, lawn mowers, brush cutters or the like.

[0023] The hand-held circular saw 10a comprises a first housing, which is configured as a motor casing 12, and a second housing 14. The hand-held circular saw 10a has a handle and a baseplate 18 for guidance of the hand-held circular saw 10a. The hand-held circular saw 10a has for its power supply a rechargeable battery (not represented in detail here). In an alternative or additional embodiment of the hand-held circular saw 10a, a mains-dependent operation of the hand-held circular saw 10a can also be provided.

[0024] The motor casing 12 encloses an interior in which at least one brushless electric motor 20 is arranged. As represented in FIG. 2, in a work operation the motor 20 rotatingly drives, via an output shaft 26 which is part of an output unit, a cutting tool 28 (cf. FIG. 1). The cutting tool 28 is here configured as a saw blade, in particular as a circular saw blade. A saw blade cover 30 protects from a touching of the cutting tool 28 and from workpiece chips of a workpiece which are flung out by the cutting tool 28 (cf. FIG. 1).

[0025] A safety braking apparatus 32 is provided to brake the cutting tool 28 as soon as an approachment of a human body part, such as, for instance, a hand, is detected with a sensor 34 of the hand-held circular saw 10a. In this illustrative embodiment, the sensor 34 is realized by a capacitively measuring sensor. The sensor 34 enables a detection of a body part nearing the cutting tool 28, on the basis of capacitive measurements (for instance by means of an alternating field), wherein, in consequence of a detection, a detection signal is generated and delivered to a control apparatus of the hand-held circular saw 10a (cable connection in FIG. 2 between sensor 34 and electronics assembly 102). Sensors of this type are known to the person skilled in the art.

[0026] The safety braking apparatus 32 has at least a first braking stage 22 and a second braking stage 24. The first braking stage 22 and the second braking stage 24, in terms of a braking effect exertable in a braking operation, are designed differently. The first braking stage 22 of the safety braking apparatus 32 is configured as an electronic braking stage 22, in that, during a braking operation, the brushless electric motor 20 is operable by means of a reversal, so that it acts as a motor brake. In this case, the electric motor 20 exerts a force on the output shaft 26, which force is directed counter to the rotation of the output shaft 26—and counter to the own rotation of the motor shaft—and thus brakes said output shaft. The thus realized first braking stage 22 is basically provided to, in a braking operation, halt a rotation of the output shaft 26 at least within the 200 milliseconds.

[0027] The second braking stage 24 is configured as a mechanical braking stage 24 having at least one mechanical braking element. As represented, the second braking stage 24 is configured as an at least two-part claw clutch having a first claw clutch part 44 (first braking apparatus part) and a second claw clutch part 46 (second braking apparatus part), wherein the first claw clutch part 44 is arranged in a substantially rotationally secure and axially movable manner on the output shaft 26. The second claw clutch part 46 is arranged in a substantially rotationally secure, in particular substantially immovable manner, in relation to the machine tool, i.e. in relation to the motor casing 12. The first claw clutch part 44 and the second claw clutch part 46 respectively have more than one toothed element 48, which are provided to, in a braking operation, intermesh (not represented in detail) and, in this way, to brake, in particular halt, a rotation of the output shaft 26. In a braking operation by means of the second braking stage 24, the first claw clutch part 44 is moved in the direction of the second claw clutch part 46 axially along the output shaft 26 (in the direction 100). As a result of the axial movement of the first claw clutch part 44 relative to the second claw clutch part 46, a coupling of first claw clutch part 44 and second claw clutch part 46 is performed, i.e. the clutch is closed. The toothed elements 48 of the first claw clutch part 44 and of the second claw clutch part 46 consequently intermesh and form a form closure. Due to the form closure, a torque directed counter to the rotation of the output shaft 26 acts between first claw clutch part 44 and second claw clutch part 46. Consequently, the rotation of the output shaft 26 and of the first claw clutch part 44 is braked, in particular halted or blocked.

[0028] In the illustrative embodiment of FIG. 2, the first claw clutch part 44 is moved by means of the actuator element 36 axially, i.e. in the direction 100. The actuator element 36 is here configured as a lifting unit, which, triggered by a current flow through the lifting unit, executes a lever movement, wherein the first claw clutch part 44 is moved in the axial direction 100. The lever movement takes place in a time of under 5 ms, in particular under 1.5 ms.

[0029] The second braking stage 24 is here basically provided to, in a braking operation, halt a rotation of the output shaft 26 within 2 milliseconds.

[0030] In an alternative illustrative embodiment, the second braking stage 24 can likewise be configured as an electronic braking stage 24, for instance analogously to the first braking stage 22 (cf. above).

[0031] In FIG. 3 is represented a flow chart, which depicts an exemplary course of a braking operation 200 using the method according to the invention for operating the safety braking apparatus 32. During the operation of the machine tool 10, in particular the hand-held circular saw 10a, the cutting tool, in the starting situation 202, rotates. In a method step 204, the approachment of a user to the cutting tool 28 is detected by means of the sensor of the sensor apparatus. Thereupon, the rotation of the output unit, in particular the output shaft 26, is braked, in particular halted, at least substantially by means of the first braking stage 22 in method step 208, after activation of the braking operation in method step 206. In method step 210, the sensor 34 detects a further approachment of the user to the cutting tool 28, in particular a touching of the cutting tool 28 by the user is detected by means of the sensor 34. Thereupon, in method step 212, an enquiry is made as to whether the cutting tool stands ready. If this is the case, the braking operation is terminated via the arrow 214, the cutting tool 28 is in the end state 220. If, on the other hand, a rotation of the cutting tool 28 is recognized, in method step 218 the rotation of the output unit, in particular the output shaft 26, is braked, in particular halted, at least substantially by means of the second braking stage 24, after the braking operation has been initiated in method step 216. This now occurring emergency braking operation by means of the second braking stage leads to halting of the cutting tool in the end state 220.