METHOD FOR PREDICTING THE REMAINING SERVICE LIFE OF A SAW BAND, AND BANDSAW MACHINE

Abstract

A method for predicting the remaining service life of a saw band in a bandsaw machine, in which a behavior or properties of the saw band clamped in the sawing machine are monitored by at least one sensor during operation of the sawing machine. Changes in the behavior or in properties of the saw band over time established on the basis of measurement signals of the sensor device are used for making a prediction about the time at which a band will break. The behavior or properties of the saw band are indirectly monitored using the at least one sensor device by way of detecting changes to components of the sawing machine which are operatively connected to the saw band.

Claims

1. A method for predicting a remaining service life of a saw band (5) in a bandsaw machine, the method comprising: monitoring a behavior or properties of the saw band (5) clamped in the sawing machine during operation of the sawing machine using at least one sensor; using changes in the behavior or in the properties of the saw band (5) over time established using measurement signals of the sensor to make a prediction about a time at which the saw band will break, and wherein the behavior or the properties of the saw band (5) are indirectly monitored using the at least one sensor by detecting changes to components of the sawing machine which are operatively connected to the saw band (5).

2. The method according to claim 1, wherein the monitoring includes indirectly sensing a lengthening of the saw band (5) using the sensor which is configured for indirectly sensing the lengthening of the saw band (5).

3. The method according to claim 1, wherein the monitoring includes detecting at least one of a change in travel at a tensioning device (8) for the saw band (5), or a change in a tension in a band guiding device (7) or an elastic deformation of the band guiding device (7) using the sensor.

4. The method according to claim 3, wherein the sensor comprises at least one of a travel sensor (9), a rotary encoder, a wire-actuated encoder, a strain gauge, or a force measuring transducer.

5. The method according to claim 3, wherein the sensor comprises a drive of the tensioning device (8) which includes an electric motor with a position encoder.

6. The method according to claim 1, wherein the monitoring includes detecting a change in travel at the tensioning device (8) for the saw band (5) using the sensor, and the method further includes generating a warning message or a prediction when a predetermined absolute limit value for a distance covered is reached or when a predetermined relative limit value for a change in travel is reached.

7. The method according to claim 6, wherein the predetermined absolute limit value for the distance covered at the tensioning device (8) is ascertained by a series of experiments using saw bands of a same type and same dimensions at a constant band tension during no-load operation until the band breaks in a manner specific to the type and dimensions as a lower value for the distance, below which value there is a defined probability of the band not breaking.

8. The method according to claim 6, wherein the predetermined relative limit value for the change in the travel is ascertained by a series of experiments using saw bands of a same type and same dimensions at a constant band tension during no-load operation until the band breaks in a manner specific to the type and dimensions as a lower value for the change, below which value there is a defined probability of the band not breaking.

9. The method according to claim 1, wherein the monitoring includes detecting a change in a tension in the band guiding device (7) or an elastic deformation of the band guiding device (7) using the sensor, and the method further includes generating a warning message or a prediction when at least one of a predetermined relative limit value for the change or a predetermined absolute limit value for the elastic deformation or tension is reached.

10. The method according to claim 9, wherein the predetermined absolute limit value for the elastic deformation of the band guiding device (7) or the tension in the band guiding device (7) is ascertained by a series of experiments using saw bands of a same type and same dimensions at a constant band tension during no-load operation until the band breaks in a manner specific to the type and dimensions as a lower value for the elastic deformation or the tension, below which value there is a defined probability of the band not breaking.

11. The method according to claim 9, wherein the predetermined relative limit value for the change in the tension in the band guiding device (7) or for the change in the elastic deformation of the band guiding device (7) is ascertained by a series of experiments using saw bands of a same type and same dimensions at a constant band tension during no-load operation until the band breaks in a manner specific to the type and dimensions as a lower value for the change, below which value there is a defined probability of the band not breaking.

12. A bandsaw machine comprising: a saw band (5) running around at least two running wheels (3, 4) and tensioned between them; a tensioner (8) for the saw band (5) that acts on at least one of the running wheels (4) and holds a tension of the saw band (5) substantially constant by changing a distance between the running wheels (3, 4); a sensor configured to detect changes to components of the sawing machine which are directly or indirectly connected to the saw band (5) in order to carrying out the method according to claim 1; and an evaluation unit configured to evaluate detected values and generate a warning message or a prediction prior to a saw band breaking.

13. The bandsaw machine according to claim 12, wherein the sensor for detecting changes to components of the sawing machine is configured to indirectly sensing a lengthening of the saw band (5).

14. The handsaw machine according to claim 12, wherein the sensor is configured to monitor at least one of a change in travel of the tensioner for the saw band (5) or a change in a tension in a band guiding device (7) or an elastic deformation of the band guiding device (7).

15. The handsaw machine according to claim 12, wherein the sensor includes at least one of a travel sensor (9), a rotary encoder, a wire-actuated encoder, a strain gauge, or a force measuring transducer.

16. The handsaw machine according to claim 12, wherein the sensor is configured to monitor a change in travel at the tensioning device (8) for the saw band (5), and the evaluation unit is configured to generate a warning message or a prediction when, as reported by the sensor, a predetermined absolute limit value for a distance covered is reached or when a predetermined relative limit value for the change in travel is reached.

17. The handsaw machine according to claim 12, wherein the sensor is configured to monitor a change in the tension in the band guiding device (7) or an elastic deformation of the band guiding device (7), and the evaluation unit is configured to generate a warning message or a prediction when, as reported by the sensor, at least one of a predetermined relative limit value for the change is reached or a predetermined absolute limit value for the elastic deformation or tension is reached.

Description

BRIEF DESSCRIPTION OF THE DRAWINGS

[0030] Exemplary embodiments of a method according to the invention and a bandsaw machine equipped according to the invention will be described and explained below with reference to the appended drawings, in which:

[0031] FIG. 1 shows a schematic view of a bandsaw machine;

[0032] FIG. 2 shows a schematic illustration of a tensioning device of the bandsaw machine according to FIG. 1;

[0033] FIG. 3 shows a schematic illustration of a band guiding device of the bandsaw according to FIG. 1;

[0034] FIG. 4 shows measurement curves of an experiment using a plurality of saw bands of the same type, measured at the tensioning device of the bandsaw machine; and

[0035] FIG. 5 shows measurement graphs of an experiment using a plurality of saw bands of the same type, measured at a band guiding device.

DETAILED DESCRIPTION

[0036] FIG. 1 schematically shows a bandsaw machine comprising a saw lower part 1, onto which a workpiece to be sawn is placed, and a saw upper part 2, which can be moved up and down relative to the saw lower part. Two running wheels 3, 4, specifically a stationary running wheel 3 and an, in this case, horizontally movable running wheel 4, of which at least one is driven, are arranged in the saw upper part 2. A saw band 5 is tensioned around these running wheels 3, 4. In order to carry out the sawing movement, said saw band runs around the two running wheels 3, 4.

[0037] In a sawing region 6 in which the saw band 5 meets a workpiece by way of the saw upper part 2 being lowered, the saw band 5 is turned by means of two band guiding devices 7 from a revolving movement plane, which is parallel to the axles of the running wheels 3, 4 and is oriented horizontally in the present case, into a cutting plane, which is oriented vertically in the present case. According to the invention, sensor devices are provided both on the adjustable running wheel 4 and also on the band guiding devices 7, as will be explained in more detail below.

[0038] FIG. 2 shows a detail from FIG. 1, specifically the adjustable running wheel 4 for the saw band 5 and an associated tensioning device 8. In the present case, said tensioning device consists of a piston/cylinder unit in order to hydraulically move the adjustable running wheel 4 outward and to hold it with a prespecified hydraulic pressure, so that the saw band 5 is tensioned with a constant tension. When the saw band 5 lengthens, the running wheel 4 is readjusted, due to the hydraulic pressure acting on the tensioning device 8, until the tension of the saw band 5 has again reached the target value.

[0039] The tensioning device 8, more precisely the piston/cylinder unit, has located on it a travel sensor 9, which can be designed as a wire-actuated encoder and connects the cylinder to an axle of the running wheel 4 in order to monitor the magnitude of the distance that the running wheel 4 covers during retensioning. The change in an average speed of the readjusting movement could also be monitored in this way.

[0040] FIG. 3 is an illustration of a detail of one of the two band guiding devices 7 of the sawing machine from FIG. 1. This band guiding device 7 consists of two band guiding rollers 10, which roll on a side surface of the saw band 5 and which transmit the forces required for revolving the saw band 5 to said saw band, and a holding plate 11 on which the band guiding rollers 10 are held and mounted. Due to the return force of the saw band 5 against the revolving caused by the band guiding rollers 10, a torque M acts on the holding plate 11, said torque causing a slight elastic deformation of the holding plate 11. A change in this deformation, which change is caused in particular by a decrease in the torsional load on the saw band 5 and therefore a decrease in the torque M, can be detected by means of a travel sensor 9, which is designed as a strain gauge and is fitted to the holding plate 11 here.

[0041] FIG. 4 shows a graph containing a plurality of measurement curves, each of which represents an experiment. The travel of an adjustment of the adjustable running wheel 4 with the tension of the saw band 5 held constant is plotted with respect to time. A plurality of saw bands in new condition were fitted into the same bandsaw machine and, respectively, onto the two running wheels 3, 4 and tensioned, after which the adjusting travel of the running wheel 4 was set to zero. The saw bands 5 were then operated on the sawing machine without load, that is to say without sawing a workpiece, until the band broke.

[0042] As can be seen with reference to FIG. 4, there was a large variation in the service life of the saw bands until the band broke, from approximately 20 hours to approximately 80 hours, even though saw bands of the same type and of the same dimensions were used, in the present case with a back height of 54 mm, on the same bandsaw machine in each case. However, according to the invention, it was found that the band always only breaks after a displacement travel of the adjustable running wheel 4 of at least 1.5 mm, irrespective of whether this was the case as early as after 20 hours or only after 30 hours.

[0043] Therefore, it is possible to make a prediction about the earliest time at which a band will break using extremely cost-effective and robust travel sensors which only have to measure to an accuracy of one tenth of a millimeter. In the present example, an absolute limit value for the distance covered of 1.4 to 1.5 mm could be used in order to be able to make a prediction that there is no need to worry about the band breaking within the next 2 to 3 hours with a high degree of probability.

[0044] FIG. 5 shows measurement graphs of measurement values which originate from the travel sensor 9, configured as a strain gauge, on the holding plate 11 of the band guiding device 7 and have been converted into a form factor that corresponds to the tension in the holding plate 11. This form factor is plotted with respect to time in hours in the graphs. Here too, different saw bands of the same type and of the same dimensions have again been operated on the same bandsaw machine without load from the new condition until the band breaks.

[0045] As can be seen in FIG. 5, the values for the form factor exhibit a clear increase approximately 1 to 3 hours before the band breaks. This can be used in order to define an absolute limit value for the form factor, the probability of a band breaking within the next 1 to 3 hours being very high above said absolute limit value. As an alternative or in addition, a relative limit value for the change in the tension can also be defined, said relative limit value once again indicating that the form factor and therefore the tension in the holding plate 11 is changing in an accelerated manner and it can be expected that the band will break within 1 to 3 hours.

[0046] Therefore, it can be seen according to the invention that it is not at all necessary to directly detect the saw band in order to monitor properties or the behavior of the saw band during operation in the sawing machine, which properties and behavior produce a conclusion in respect of how long it would be until there is a risk of the band breaking and therefore allow a prediction to be made about the time at which a band will break. Rather, it suffices to detect changes to components of the sawing machine which are operatively connected to the saw band.

[0047] Furthermore, a simple relationship between a very probably imminent situation of the band breaking and an increasing lengthening of the saw band or a decreasing torsional load on said saw band during operation of the sawing machine has been identified within the scope of the present invention, wherein these properties of the saw band can be indirectly identified at components which are operatively connected to the saw band. Therefore, according to the invention, it is no longer necessary to directly monitor the saw band by means of sensor systems that are complicated and susceptible to faults.

LIST OF REFERENCE SIGNS

[0048] 1 Saw lower part

[0049] 2 Saw upper part

[0050] 3 Running wheel (fixed)

[0051] 4 Running wheel (adjustable)

[0052] 5 Saw band

[0053] 6 Sawing region

[0054] 7 Band guiding device

[0055] 8 Tensioning device

[0056] 9 Travel sensor

[0057] 10 Band guiding rollers

[0058] 11 Holding plate

[0059] F Force

[0060] M Torque