Device For Predicting Blade Breakage Of A Bandsaw Blade Of A Bandsaw

Abstract

A device for predicting a blade breakage of a bandsaw blade of a bandsaw. The device comprises an eddy-current sensor configured to generate a sensor signal that is dependent on a technical parameter of the bandsaw blade. The device further comprises an evaluation unit configured to evaluate the sensor signal, to compare the sensor signal with a predetermined tolerance range, and to generate a warning signal that indicates an imminent blade breakage of the bandsaw blade if the sensor signal lies outside of the predetermined tolerance range.

Claims

1. A device for predicting a blade breakage of a bandsaw blade of a bandsaw, the device comprising: an eddy-current sensor configured to generate a sensor signal that is dependent on a technical parameter of the bandsaw blade; and an evaluation unit configured to evaluate the sensor signal, to compare the sensor signal with a predetermined tolerance range, and to generate a warning signal that indicates an imminent blade breakage of the bandsaw blade if the sensor signal lies outside of the predetermined tolerance range.

2. The device as claimed in claim 1, wherein the evaluation unit is configured to determine the technical parameter based on the sensor signal.

3. The device as claimed in claim 1, wherein the evaluation unit is configured to electronically filter the sensor signal before comparing the sensor signal with the predetermined tolerance range.

4. The device as claimed in claim 1, wherein the evaluation unit is configured to electronically smooth the sensor signal before comparing the sensor signal with the predetermined tolerance range.

5. The device as claimed in claim 1, wherein the technical parameter comprises a dimensional property of the bandsaw blade.

6. The device as claimed in claim 1, wherein the evaluation unit is configured to determine from the sensor signal, as the technical parameter, a saw blade thickness of the bandsaw blade, and to generate the warning signal if the saw blade thickness is outside of the predetermined tolerance range.

7. The device as claimed in claim 1, wherein the eddy-current sensor is configured to generate the sensor signal while the bandsaw blade is executing a revolving motion.

8. The device as claimed in claim 1, wherein the eddy-current sensor is configured to generate a magnetic field oriented perpendicularly to a blade surface of the bandsaw blade, the magnetic field inducing in the bandsaw blade a voltage that causes eddy currents.

9. The device as claimed in claim 8, wherein the evaluation unit is configured to determine an amplitude of the eddy currents based on the sensor signal, and to generate the warning signal if the amplitude of the eddy currents exceeds the predetermined tolerance range.

10. The device as claimed in claim 8, wherein the evaluation unit is configured to determine a phase of the eddy currents based on the sensor signal, and to generate the warning signal if the phase of the eddy currents exceeds the predetermined tolerance range.

11. A bandsaw, comprising: a first bandsaw wheel rotatably mounted about a first rotation axis; a second bandsaw wheel rotatably mounted about a second rotation axis, the second rotation axis being arranged parallel to and spaced apart from the first rotation axis; a bandsaw blade that is guided over the first bandsaw wheel and the second bandsaw wheel so as to execute a revolving motion around the first bandsaw wheel and the second bandsaw wheel; and a device for predicting a blade breakage of the bandsaw blade, the device comprising: an eddy-current sensor configured to generate a sensor signal that is dependent on a technical parameter of the bandsaw blade; and an evaluation unit configured to evaluate the sensor signal, to compare the sensor signal with a predetermined tolerance range, and to generate a warning signal that indicates an imminent blade breakage of the bandsaw blade if the sensor signal lies outside of the predetermined tolerance range.

12. The bandsaw as claimed in claim 11, wherein the eddy-current sensor comprises a transmitter and a receiver, the transmitter and the receiver being arranged on a same side of the bandsaw blade.

13. The bandsaw as claimed in claim 11, wherein the eddy-current sensor comprises a transmitter and a receiver, the transmitter and the receiver being arranged on mutually opposite sides of the bandsaw blade.

14. The bandsaw as claimed in claim 11, wherein the evaluation unit is configured to determine the technical parameter based on the sensor signal.

15. The bandsaw as claimed in claim 11, wherein the evaluation unit is configured to electronically filter the sensor signal before comparing the sensor signal with the predetermined tolerance range.

16. The bandsaw as claimed in claim 11, wherein the evaluation unit is configured to electronically smooth the sensor signal before comparing the sensor signal with the predetermined tolerance range.

17. The bandsaw as claimed in claim 11, wherein the technical parameter comprises a dimensional property of the bandsaw blade.

18. The bandsaw as claimed in claim 11, wherein the evaluation unit is configured to determine from the sensor signal, as the technical parameter, a saw blade thickness of the bandsaw blade, and to generate the warning signal if the saw blade thickness is outside of the predetermined tolerance range.

19. The bandsaw as claimed in claim 11, wherein the eddy-current sensor is configured to generate the sensor signal while the bandsaw blade is executing a revolving motion.

20. The bandsaw as claimed in claim 11, wherein the eddy-current sensor is configured to generate a magnetic field oriented perpendicularly to a blade surface of the bandsaw blade, the magnetic field inducing in the bandsaw blade a voltage that causes eddy currents.

Description

DRAWINGS

[0050] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0051] FIG. 1 is a schematic view of an example of a device for predicting a blade breakage according to the present disclosure, and of an example of a bandsaw including the device;

[0052] FIG. 2 is a planar view of an example of a bandsaw blade included in the bandsaw of FIG. 1; and

[0053] FIG. 3 is a schematic view of an example of an eddy-current sensor according to the present disclosure.

[0054] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

[0055] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0056] FIG. 1 schematically shows a bandsaw 100 comprising a device 10 for predicting a blade breakage. The bandsaw 100 has a bandsaw stand 11, arranged on which, preferably mounted in a rotatable manner, there is a first and a second bandsaw wheel 12, 14. The first and second bandsaw wheels 12, 14 rotate about two axes of rotation 16, 18 that are spaced apart from one another in the vertical direction, the axes of rotation 16, 18 extending orthogonally into the blade plane at the respective center of the cross in the view shown here.

[0057] The first and the second bandsaw wheel 12, 14 may be, for example, a roller or a drum. Preferably, at least one of the bandsaw wheels 12, 14 is motor-driven.

[0058] A motor drive of the bandsaw wheels 12, 14 may be realized, for example, by an internal combustion engine, a pneumatically or hydraulically operating motor or an electric motor. In further embodiments, a drive may also additionally have a gear unit by means of which the rotational speed between a motor output shaft and the respective bandsaw wheel 12, 14 to be driven can be varied.

[0059] A bandsaw blade 20 is guided over the two bandsaw wheels 12, 14 in such a manner that it is set in a revolving motion around the first and second bandsaw wheels 12, 14, along a sawing direction 22, when the first and second bandsaw wheels 12, 14 rotate about their respective axis of rotation 16, 18. In the shown embodiment, the rotational motion of the two bandsaw wheels 12, 14 is counter-clockwise.

[0060] The bandsaw blade 18 has a toothed side 24 and a non-toothed side 26 (see FIG. 2). The toothed side 24 is often referred to as the tooth side and the non-toothed side 26 as the blade back. The toothed side 24 has a multiplicity of saw teeth configured to cut a material 28 to be sawed. The material 28 to be sawed is guided along a feed direction (not shown here) parallel to the axes of rotation 16, 18 onto the toothed side 24 of the bandsaw blade 20, and is sawed up by the multiplicity of saw teeth. The material 28 to be sawed may be, for example, a whole tree trunk, a board or any other object to be sawed. In other embodiments, the bandsaw blade 20 may also be toothed on both sides or toothless, e.g. diamond-coated for cutting stones.

[0061] In order to ensure safe and stable guiding of the bandsaw blade 20 on the bandsaw wheels 12, 14, the bandsaw blade 20 is (mechanically) tensioned between the first bandsaw wheel 12 and the second bandsaw wheel 14. For the purpose of tensioning the bandsaw blade 20, for example the first and/or second bandsaw wheel 12, 14 is/are moved away from each other along a tensioning path 30, which is illustrated in FIG. 1 by means of a double arrow.

[0062] During the machining process, the bandsaw blade 20 is subject to a constant, very high mechanical and thermal stress, which can cause blade cracks 32, 33 (see FIG. 2) in the bandsaw blade 20 in microscopic and macroscopic form. These blade cracks 32, 33 pose a risk to the sawing process, as they can result in a blade breakage, which can destroy parts of the bandsaw 100.

[0063] For early prediction of a blade breakage of the bandsaw blade 20, the bandsaw 100 comprises the device 10. The device 10 comprises an eddy-current sensor 34, which is configured to generate a sensor signal that is dependent on and indicates a technical parameter of the bandsaw blade 20. The sensor signal is transmitted via one or more cables or wirelessly to an evaluation unit 36.

[0064] The eddy-current sensor 34 is preferably a commercially available eddy-current sensor. Preferably, the eddy-current sensor 34 is configured to sense the technical parameter of the bandsaw blade 20 while the bandsaw blade 20 revolves around the two bandsaw wheels 12, 14 at a sawing speed of, for example, 50 meters per second (m/s). The eddy-current sensor 34 is preferably oriented in such a manner that an effective direction 38 of the eddy-current sensor 34 is substantially perpendicular (for example ±5%) to at least one of the two axes of rotation 16, 18 and the sawing direction 22 (see FIG. 3). The effective direction 38 defines, as it were, a normal direction to a blade surface 39 of the bandsaw blade 20.

[0065] The evaluation unit 36 is configured to evaluate the sensor signal, to compare it with a predetermined tolerance range 40 (FIG. 2) and to generate a warning signal indicating an imminent blade breakage of the bandsaw blade 20 if the sensor signal lies outside of the predetermined tolerance range 40. The predetermined tolerance range 40 may be defined, for example, by a tolerable 10% deviation from a tolerance value 42. The warning signal may be generated as an audible sound signal or displayed as a visual message “Attention blade breakage” on a screen.

[0066] The technical parameter may be, for example, a dimensional property of the bandsaw blade 20, preferably a saw blade thickness 44. In this case, the tolerance value 42 describes a bandsaw-blade limit thickness. In this case, the tolerance range 40 is defined by a tolerable, e.g. 10%, deviation from the bandsaw-blade limit thickness.

[0067] Alternatively, the technical parameter may also be an amplitude and/or phase of the eddy current sensed by the eddy-current sensor 34. If the sensed eddy current exceeds a predetermined limit value (for example, taking into account a 10% deviation), the warning signal is output by the evaluation unit 36.

[0068] Represented in FIG. 2, in addition to the bandsaw blade 20, there is also an exemplary diagram 46, from which an exemplary (graphic) evaluation of the sensor signal is represented. In the diagram 46, for greater clarity, a curve 48 of the saw blade thickness 44 (abscissa) is plotted over a saw blade length 50 (ordinate) of the bandsaw blade 20 running parallel to the sawing direction 22. As a rule, however, crack detection is preferably effected by the evaluation of anomalies in the sensor signal, for example can be determined by evaluation of the amplitude and/or phase of the eddy current sensor signal.

[0069] It can be seen that the saw blade thickness 44 decreases in the course of the length at the point where the blade breakage 33 occurs, down to the tolerance value 42, i.e. the saw-blade limit thickness, but is still within the tolerance range 40. Thus, preferably no warning signal is output at this point, but the evaluation unit already recognizes that this point in the course of the length of the bandsaw blade 20 marks a critical point for blade breakage.

[0070] Preferably, the eddy-current sensor monitors the blade thickness 44 of the bandsaw blade 20 over an entire width 52 of the bandsaw blade.

[0071] In FIG. 3, the device 10 has a control unit 54 in addition to the evaluation unit 36. The evaluation unit 36 is configured to transmit the warning signal to the control unit 54 via one or more cables or wirelessly. The control unit 54 is configured to switch off the bandsaw 100 when it receives the warning signal.

[0072] Preferably, it is possible for the evaluation unit 36 to generate different warning signals, each indicating different stages of an incipient blade crack 32, 33 of the bandsaw blade 18. It is advantageous if, for example, a first warning signal is generated by the evaluation unit 36 when first signs of an incipient blade crack 32, 33 are detected (as is the case, for example, in FIG. 2 in diagram 46), and a second warning signal is generated when a blade crack 32, 33 is already in an advanced stage (in the case of diagram 46, for example, falls below the tolerance value 42 (e.g., by more than 10%). In this case, for safety reasons, the bandsaw 100 may be switched off by the control unit 54 or manually by an operator. Such a cascaded warning signal makes it possible, for example, to inform an operator about a stage of an impending blade breakage. If the blade crack 32, 33, for example, reaches an order of magnitude of ⅓ of the blade width 52 of the bandsaw blade 20, the bandsaw 100 is switched off immediately.

[0073] Further, the eddy-current sensor 34 has a transmitter 56 and a receiver 58. The transmitter 56 is configured to generate a magnetic field oriented perpendicularly to the blade surface 39 of the bandsaw blade 20, the field lines of which penetrate the blade surface 39 of the bandsaw blade 20 in an effective direction between the two field poles, and penetrate it completely in the thickness direction of the bandsaw blade 20. The transmitter 56 and the receiver 58 are located on one and the same side of the bandsaw blade 20.

[0074] The receiver 58 is preferably configured to detect a strength of the magnetic field generated by the transmitter 56, minus the Joule eddy-current losses generated when penetrating the bandsaw blade 20, or merely the eddy currents generated in the bandsaw blade by induction, in the form of the sensor signal.

[0075] It is to be noted that the features shown in the above embodiments may be used in other embodiments in a modified form, as well as alternatively or complementarily to each other, or even that individual features do not have to be present.

[0076] Thus, for example, the arrangement of the individual features may vary, without departing from the spirit and scope of the present disclosure. In other embodiments, for example, one of the axes of rotation 16, 18 may be configured such that it can be inclined relative to the other axis of rotation 16, 18, such that the two axes of rotation 16, 18 in these embodiments are not parallel to each other. Moreover, in other embodiments, both bandsaw wheels 12, 14 may also be motor-driven. Likewise, it is not absolutely necessary to orient the two bandsaw wheels 12, 14 vertically with respect to each other. Moreover, it should be mentioned that the device 10 can be used with any type of bandsaw, which may also have, for example, a bandsaw blade that is toothed on both sides, in order thus to be able to saw workpieces both along and contrary to the feed direction.

[0077] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.