SE541451C2

SE541451C2 - Chainsaw lubrication need detection

Info

Publication number: SE541451C2
Application number: SE1850184A
Authority: SE
Inventors: Hans-Åke Sundberg
Original assignee: Husqvarna Ab
Priority date: 2018-02-20
Filing date: 2018-02-20
Publication date: 2019-10-08
Also published as: SE1850184A1; DE102019103804A1

Abstract

A chainsaw comprises a guide bar (2); an endless cutting chain (3) which is mounted so as to turn around the guide bar (2); a drive motor (6) for driving the cutting chain (3); a detection arrangement (8) configured to detect the need of lubrication of the cutting chain (3); and a signal processing arrangement (10) for processing information from the detection arrangement (8), wherein the detection arrangement (8) comprises a sensor arrangement (9) comprising a first acoustic sensor (9a), the sensor arrangement (9) being configured to sense a friction relating to the cutting chain (3) and the guide bar (2) by measuring an acoustic noise generated by said friction when said cutting chain is operated to turn around said guide bar.

Description

CHAINSAW LUBRICATION NEED DETECTION TECHNICAL FIELD The present invention relates to a method for detecting the need of lubrication of a cutting chain of a chainsaw and for processing information based thereon. The present invention also relates to a chainsaw comprising, inter alia, a detection arrangement for detecting the need of lubrication of the cutting chain, and a signal processing arrangement for processing information from the detection arrangement.

BACKGROUND OF THE INVENTION It is already known in the prior art to sense and indicate and/or control the need of lubrication of a cutting chain of a chainsaw.

E.g. US 2010/0043234 A1 suggests a chainsaw provided with an electronic lubrication pump, which is operated based on e.g. the current consumed by the drive motor of the cutting chain or the torque of the motor, the temperature of the guide bar, the flow rate of lubricating fluid, or the level of the lubricating fluid in a storage tank.

There is however, a need for a more reliable method of detecting the need of lubrication of the cutting chain, to allow improved operation and/or reduced consumption of lubrication fluid.

SUMMARY OF THE INVENTION It is an object of to solve, or at least mitigate, the above-mentioned problem. To this end, there is provided a chainsaw comprising a guide bar; an endless cutting chain which is mounted so as to turn around the guide bar; a drive motor for driving the cutting chain; a detection arrangement configured to detect the need of lubrication of the cutting chain; and a signal processing arrangement for processing information from the detection arrangement, the chainsaw being characterized in that said detection arrangement comprises a sensor arrangement comprising a first acoustic sensor, the sensor arrangement being configured to sense a friction relating to the cutting chain and the guide bar by measuring an acoustic noise generated by said friction when said cutting chain is operated to turn around said guide bar. Such a sensor arrangement may be configured for sensing the friction between members of the cutting chain and/or between the cutting chain and the guide bar, which allows controlling a lubrication of the cutting chain on a lubrication need basis.

According to an embodiment, said first acoustic sensor may be configured to resonate at an acoustic noise frequency of said friction. Thereby, a strong and accurate friction signal may be obtained.

According to an embodiment, said first acoustic sensor may be configured to resonate at an ultrasonic resonance frequency, e.g. between 20 and 1000 KHz; preferably, more than 50 kHz; and more preferably, between 100 and 500 KHz. Similarly, also any second acoustic sensor of the sensor arrangement may optionally be configured to resonate at an ultrasonic resonance frequency, e.g. between 20 and 1000 KHz; preferably, more than 50 kHz; and more preferably, between 100 and 500 KHz. Metal-to-metal friction generates a characteristic acoustic noise, sometimes termed acoustic emissions, at such ultrasonic frequencies.

According to an embodiment, said first acoustic sensor may be a piezoelectric sensor. Similarly, also any second acoustic sensor of the sensor arrangement may optionally be a piezoelectric sensor. Any such piezoelectric sensor may be configured as a broadband sensor having a bandwidth of more than 1.1 MHz. Additionally or alternatively, said first and/or second acoustic sensor(s) may be a MEMS sensor.

According to an embodiment, the detection arrangement may be mounted on the chainsaw in physical contact with the guide bar, or directly on the guide bar. Thereby, acoustic emissions may be picked up from a body which is integrally formed with the friction source, i.e. the engagement between cutting chain and guide bar.

According to an embodiment, said sensor arrangement may be configured to provide a first noise signal, indicative of the noise generated by the friction relating to the cutting chain and the guide bar, to the signal processing arrangement. The sensor arrangement may also comprise a second acoustic sensor configured to measure the acoustic noise generated by the friction relating to the cutting chain and the guide bar, wherein said second sensor is configured to provide a second noise signal indicative thereof to the signal processing arrangement.

According to an embodiment, said first and second acoustic sensors may have different resonance frequencies. The frequencies may be tuned to a respective friction noise frequency of a respective friction source. By way of example, the first acoustic sensor may be tuned to a friction noise frequency of the engagement between the cutting chain and the guide bar, whereas the second acoustic sensor may be tuned to a friction noise frequency of the engagement between cutting chain links. Thereby, the wear situation of different parts of the chainsaw may be monitored.

According to an embodiment, said signal processing arrangement may be configured to compare said first noise signal with a noise signal reference value, and provide an event signal based on said noise signal exceeding said noise signal reference value. Similarly, the signal processing arrangement may be configured to compare the noise signal of any second acoustic sensor with a noise signal reference value, which may be the same as or different from the noise signal reference value to which the first noise signal is compared, and provide an event signal based on second said noise signal exceeding the respective noise signal reference value. The signal processing arrangement may further be configured to determine a rate of event signals and generate a lubrication signal based on the event signal rate exceeding a reference event signal rate. The rate of event signals may, by way of example, be based on a number of event per period of time, a number of events per chain travel distance unit, or any other suitable representation of an event signal rate. Alternatively, the lubrication signal may be generated directly based on a detected noise signal, such as by indicating a noise level to a user, or based on an event signal, without determining an event signal rate. The lubrication signal may be used for indicating a lubrication need to a user, e.g. using any suitable type of indicator, and/or for automatically triggering at least one of a lubrication pump, configured to feed a lubricating fluid towards at least one point along the assembly of the cutting chain and the guide bar, and a lubrication valve, configured to control a flow of lubricating fluid to at least one point along the assembly of the cutting chain and the guide bar. According to embodiments, the lubrication signal may be generated based on a mean value of the rate of event signals, or based on a mean value the noise signal.

According to an embodiment, said signal processing arrangement may be configured to generate a lubrication signal based on an RPM (rotation speed) of the drive motor. By way of example, the signal processing arrangement may be configured to trigger a friction determination, using signals from the sensor arrangement, at one or more predetermined RPMs. Alternatively or additionally, the RPM may be used for determining a free-running condition, for example by comparing a rate of change of the RPM with a rate of change of an event signal rate as defined hereinabove.

According to an embodiment, the chainsaw may further comprise an indicator which is operatively connected to the sensor arrangement and configured for indicating, to a user, the need of lubrication of the cutting chain in response to said noise signal. The indicator may, for example be configured as a light emitting diode (LED) or a buzzer configured to emit an audio signal.

According to an embodiment, said signal processing arrangement is configured to, based on a detected change or lack of change of friction following a lubrication, indicate a possible need for adjustment of the tension of the cutting chain. By way of example, if the amount of friction remains above a reference value after lubricating the chain, this may be an indication of an overly tensioned cutting chain.

Another object is to provide a method allowing lubrication to become more efficient and the required amount of lubricating fluid is minimized. It will thereby be possible e.g. to reduce the volume of a storage tank for the lubricating fluid or the time between refilling will be longer. The more efficient lubrication and the minimized amount of lubricating fluid also lead to reduced environmental influence and working expenses.

Accordingly, such a method may comprise operating the cutting chain to turn about a guide bar; measuring an acoustic noise generated by friction when said cutting chain is operated to turn around said guide bar; and, based on the measured acoustic noise, generating a first noise signal. The noise signal may be indicated a lubrication need to a user, or may be used for automatically triggering a lubrication of the chain. The signal may also be further processed to provide improved detection. The method may involve sensing the friction between members of the cutting chain and/or between the cutting chain and the guide bar.

When receiving an indication that lubrication is needed, the operator of the chainsaw, or a controller, may perform lubrication by operating a pump for feeding a lubricating fluid towards at least one point of assembly of the cutting chain and the guide bar or by operating a valve for opening and closing the feeding of a lubricating fluid to said pump.

It should be noted that an indication that lubrication is needed, may also implicitly indicate that lubrication is not working properly e.g. due to a stop in the feeding channels for the lubricating fluid, or that the storage tank for the lubricating fluid is empty. If despite operation of the pump for feeding the lubricating fluid to the cutting chain or of the valve in connection with said pump, the indication that lubrication is needed is maintained, the operator may be prompted to control the storage tank as well as the feeding channels for the lubricating fluid.

According to an embodiment, measuring the acoustic noise may comprise measuring the acoustic noise at an ultrasonic frequency, for example of between 20 and 1000 KHz; preferably, more than 50 kHz; and more preferably, between 100 and 500 KHz.

The measurement may involve emphasizing or discriminating the signal at a specific frequency or frequency range, for example by means of resonant detection. Resonant detection may be obtained by using an acoustic sensor configured to resonate at a frequency or set of frequencies within any of the above frequency ranges. Alternatively, the signal may be filtered using any suitable digital or analogue filter, such as a lowpass or bandpass filter.

According to an embodiment, said sensor arrangement may be configured to provide a first noise signal, which may be indicative of the noise generated by the friction relating to the cutting chain and the guide bar, to a signal processing arrangement.

According to an embodiment, measuring the acoustic noise may comprise measuring the acoustic noise at two spatially separated positions. Thereby, different noise signals may represent different friction sources, such as nose sprocket friction, friction between chain links, and friction between guide bar and chain.

According to an embodiment, measuring the acoustic noise may comprise measuring the acoustic noise at two separate frequencies. The two frequencies may e.g. correspond to two predetermined noise frequencies of the friction noise. Alternatively, one of the frequencies may correspond to a frequency of the friction noise, whereas the other frequency may correspond to a frequency outside the friction noise, for comparison.

According to an embodiment, the method may further comprise comparing said first noise signal with a noise signal reference value and, based on the noise signal exceeding said noise signal reference value, generating at least one event signal.

According to an embodiment, the method may further comprise counting a rate of event signals and, based on the event signal rate exceeding an event signal reference rate, generating a lubrication signal. The rate of event signals may, by way of example, be based on a number of event per period of time, a number of events per chain travel distance unit, or any other suitable representation of event signal rate. Alternatively, the lubrication signal may be generated directly based on a detected noise signal, such as by indicating a noise level to a user, or based on an event signal, without determining an event signal rate. The lubrication signal may be used for indicating a lubrication need to a user, e.g. using any suitable type of indicator, and/or for automatically triggering at least one of a lubrication pump, configured to feed a lubricating fluid towards at least one point along the assembly of the cutting chain and the guide bar, and a lubrication valve, configured to control a flow of lubricating fluid to at least one point along the assembly of the cutting chain and the guide bar. The lubrication signal may be generated based on a mean value of said rate of event signals.

According to an embodiment, the method may comprise determining whether the chainsaw is free-running; and, based on said determination, determining whether there is a need for lubrication of the cutting chain. Said determination of whether the chainsaw is free-running may be made by, for example, comparing a change of a noise signal with a change of an RPM of the chainsaw. An increase of a noise level combined with a decrease of RPM indicates a loaded condition, i.e. the chainsaw is cutting. If there is no indication of a loaded condition, the chainsaw may be assumed to be free-running.

According to an embodiment, the method may further comprise indicating, to a user, the need of lubrication of the cutting chain.

According to an embodiment, the method may further comprise indicating, based on a detected change or lack of change of friction following a lubrication, a possible need for adjustment of the tension of the cutting chain.

The above method, as well as and the above described detection and signal processing arrangements of the chainsaw, may be used for indicating a possible need for adjustment of the tension of the cutting chain.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be further described below with reference to the accompanying drawings, in which Fig. 1 is a schematic view of a chainsaw comprising a first embodiment of a detection arrangement and a signal processing arrangement; Fig. 2 is a schematic view of a chainsaw comprising a second embodiment of a detection arrangement and a signal processing arrangement; Fig. 3 is a schematic view of a chainsaw comprising a third embodiment of a detection arrangement and a signal processing arrangement, Fig. 4 is a schematic view of a chainsaw comprising a fourth embodiment of a detection arrangement and a signal processing arrangement; Fig. 5 is a schematic view of a chainsaw comprising a fifth embodiment of a detection arrangement and a signal processing arrangement; and Fig. 6 is a schematic diagram illustrating an RPM and an event signal rate of a chainsaw revving up.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS As mentioned above, the present invention relates to a method for detecting the need of lubrication of a cutting chain of a chainsaw and for processing information based thereon. The present invention also relates to a chainsaw which comprises means for performing these detecting and processing steps.

The chainsaw may be of any conventional type, comprising, inter alia, a main body 1, a guide bar 2 around which an endless cutting chain 3 is mounted, a front handle 4, a rear handle 5, a drive motor 6 for driving the cutting chain 3 to turn around the guide bar 2 and a pump 7 for feeding a lubricating fluid from a storage tank (not illustrated in the drawings) towards at least one point along the assembly of the cutting chain 3 and the guide bar 2, i.e. towards at least one point on the guide bar close to the cutting chain and/or between the guide bar and the cutting chain, e.g. in the groove for the cutting chain on said guide bar. The drive motor 6 may typically be an electric motor, which may optionally be battery powered, or an internal combustion engine.

The chainsaw further comprises a detection arrangement 8 for detecting the need of lubrication of the cutting chain 3. The detection arrangement 8 comprises in turn a sensor arrangement 9. This sensor arrangement 9 is configured for sensing the friction relating to the cutting chain 3 and the guide bar 2 on which the cutting chain is mounted.

Accordingly, the sensor arrangement 9 is configured for sensing the friction between members of the cutting chain 3, e.g. the rivets and drive and cutting links thereof. In addition to this internal cutting chain friction, or as an alternative thereto, the friction between the cutting chain 3 and the guide bar 2 may be sensed. Sensing of the friction between the cutting chain 3 and members of and on the guide bar 2 such as the nose wheel and the drive sprocket on the guide bar, is thereby also possible. Sensing is performed when said cutting chain 3 is operated to turn around said guide bar 2. The sensor arrangement 9 provides at least one noise signal A which is indicative of this friction between the cutting chain members and/or the cutting chain 3 and the guide bar 2. The sensor arrangement 9 is configured for sensing the friction between the cutting chain members and/or the cutting chain 3 and the guide bar 2 by measuring the acoustic noise generated by said friction, and for providing the at least one noise signal A based thereon. As used herein, the term “acoustic” shall be construed as relating to mechanical waves such as vibration, sound, ultrasound and infrasound. The sensor arrangement 9 comprises thereby at least one acoustic sensor 9a (see fig. 1 and 2) for measuring the noise generated by the friction between the cutting chain members and/or the cutting chain 3 and the guide bar 2.

Alternatively, the sensor arrangement 9 may comprise two or more acoustic sensors 9b and 9c (see fig. 3 and 4) for measuring the noise generated by the friction between the cutting chain members and/or the cutting chain 3 and the guide bar 2 and providing two or more noise signals A1 and A2 indicative thereof.

The acoustic sensors 9a; 9b, 9c may be acoustic emission (AE-) sensors. They may be piezoelectric sensors configured for sensing a resonance frequency within an interval of e.g. 50-1000 kHz, and preferably within the interval 100-500 kHz, or e.g. piezoelectric broadband sensors which are configured for sensing frequencies up to about 1 ,1 MHz. Sensors of MEMS (microelectromechanical system) type may also be used. In case of two or more acoustic sensors 9b, 9c, the acoustic sensors may have different resonance frequencies, and may optionally be of different types. The sensing arrangement 9 may also comprise one or several temperature sensors (not illustrated), which may optionally be co-located with the acoustic sensor(s), thereby allowing the signal processing arrangement 10 to compensate for any temperature drift.

As illustrated in the drawings, the sensor arrangement 9 in the form of the acoustic sensors 9a; 9b, 9c is mounted on the guide bar 2 of the chainsaw. Alternatively, the sensor arrangement 9 may be mounted anywhere on the chainsaw, on the outside as well as the inside thereof, as long as it in some way is in mechanical contact with the guide bar 2.

The chainsaw further comprises a signal processing arrangement 10 for processing the information from the detection arrangement 8, i.e. the at least one noise signal A from the sensor arrangement 9.

The signal processing arrangement 10 comprises in the illustrated embodiments according to fig. 1 and 2 a comparing means 11 which, for example, may be configured as an electronic comparator. This comparing means 11 is in the illustrated embodiments according to fig. 1 and 2 operatively connected to the sensor arrangement 9 by means of an electric lead 12a. The connection between the comparing means 11 and the sensor arrangement 9 may alternatively be wireless. The comparing means 11 is configured for comparing the noise signal A with a reference value thereof, in the following referred to as a noise signal reference value, defining a predetermined or dynamically set noise level, and for providing at least one event signal B each time the noise signal exceeds said noise signal reference value.

In case of a sensor arrangement 9 which comprises two or more acoustic sensors 9b, 9c, the comparing means 11 is operatively connected to the sensor arrangement 9 by means of two or more electric leads 12b and 12c (see fig. 3 and 4) for comparing each of the two or more noise signals A1, A2 with a respective reference value thereof. The connection between the comparing means 11 and the sensor arrangement 9 may alternatively be wireless. The comparing means may in this case comprise two or more comparing units 11a and 11b, which may be configured as respective electronic comparators, whereby each comparing unit 11a, 11b compares one of the noise signals A1 or A2 with the reference value for said noise signal. The comparing means 11 provides an event signal B1 and B2 respectively, each time the respective noise signal A1, A2 exceeds the reference value thereof.

The detection arrangement 8, and the signal processing arrangement 10 forming part of the chainsaw, is in the illustrated embodiments powered by a voltage of e.g. 5V, either from an external power source, from the chainsaw, from a battery or from within the detecting means 8. Therefore, the event signals B; B1, B2 provided by the comparing means 11 may consist of a 5V voltage, and the noise signal reference value of the noise generated by the friction between the cutting chain members and between the cutting chain 3 and the guide bar 2, and to be exceeded by the noise signals A; A1, A2 for providing the event signals B; B1, B2, may be set to a fixed voltage of less than 5 V, such as about 2,5 V. However, the detection and signal processing arrangements 8, 10 of the chainsaw may be powered with any other suitable voltage and the noise signal reference value, to be exceeded by the noise signals A; A1, A2, may be set to any other suitable voltage. The noise signal reference value may be statically set. Alternatively, it may be dynamically set based on e.g. historic values of the noise signal(s) A; A1, A2 in order to detect a change in noise level.

It should be noted that respective noise signal reference values, to be exceeded by the noise signals A; A1, A2, may be individually set for calibrating the respective trigger sensitivities of the acoustic sensors 9a; 9b, 9c. This may be particularly useful when two or more acoustic sensors with different sensitivity are used, which also reduces the costs for the acoustic sensors.

The signal processing arrangement 10 of the chainsaw further comprises a calculating means 13, which may be configured as an electronic counter, and which may comprise an oscillator for generating a time base, to operate as a frequency counter. The calculating means 13 is in the illustrated embodiments according to fig. 1 and 2 operatively connected to the comparing means 11 by means of an electronic lead 14a. The connection between the calculating means 13 and the comparing means 11 may alternatively be wireless. The calculating means 13 is configured for counting the number of event signals B per time period and providing a lubrication signal C each time the number of event signals B per time period exceeds a reference number thereof per time period, i.e. when the event signal rate exceeds an event signal reference rate. It should be noted that each of the signals A, B, and C is representative of the friction level as detected by the sensor arrangement 9, albeit with an increasing level of signal processing.

Alternatively, the calculating means 13 may be configured for counting the number of second signals B per chain travel distance unit, i.e. the number of event signals B generated during a certain defined distance of travel or movement of the cutting chain 2, and providing a lubrication signal C each time the number of event signals B per chain travel distance unit exceeds a reference number thereof per chain travel distance unit, i.e., again, an event signal reference rate. By knowing the rpm of the cutting chain 3, it is possible to calculate or directly measure the number of event signals B during each chain travel distance unit. The chain travel distance unit may vary as required for achieving the best possible result. It may be one revolution or less than one revolution, e.g. a few mm. It may also be more than one revolution. According to such an embodiment, e.g. the drive motor 6, or drive electronics for driving the drive motor 6, may generate a chain speed dependent timebase for defining a gate time of a frequency counter.

The lubrication signal C is in the embodiment according to fig. 1 provided for indicating by means of an indicator 15 the need of lubrication of the cutting chain 3. This indicating means 15 can be integrated in the calculating means 13 if desired. With this embodiment, an operator has the opportunity to manually activate the pump 7 for feeding a lubricating fluid towards at least one point along the assembly of the cutting chain 3 and the guide bar 2 or to activate a valve (not illustrated in the drawings) for opening and closing the feeding of lubricating fluid to said pump 7. This valve may be located in any position in the feeding channel between the storage tank for the lubricating fluid and the lubrication fluid delivery point at the chain 3. When using a valve, it is possible to let the pump operate continuously. The chainsaw may be configured to completely close the valve when the chainsaw is not operating, such that any leakage of lubrication fluid is minimized.

Alternatively, in the embodiment according to fig. 2, the lubrication signal C is instead provided for triggering activation of the pump 7 for feeding a lubricating fluid towards at least one point along the assembly of the cutting chain 3 and the guide bar 2 or for triggering activation of the valve for opening and closing the feeding of lubricating fluid to said pump 7. Thus, with this embodiment, the pump 7 or the valve in connection with the pump is automatically activated. The lubrication signal C is in the illustrated embodiment transmitted to the pump 7 through a line 16, but may also be transmitted wirelessly.

In the embodiments of fig. 3 and 4, the calculating means 13 is operatively connected to the comparing means 11 by means of two electric leads 14b and 14c, such that the comparing means 11 can provide an event signal B1 and B2 respectively, on each lead 14b, 14c. The connection between the calculating means 13 and the comparing means 11 may alternatively be wireless. With the comparing means 11 providing an event signal B1 and B2 respectively, each time a respective noise signal A1, A2 exceeds the reference value thereof, the calculating means 13 is configured for counting the number of each event signal B1, B2 per time period, and for calculating a mean value MV of said numbers and providing a lubrication signal C each time said mean value MV exceeds a predetermined or dynamically set reference mean value. The calculating means 13 may here comprise two or more counting units 13a and 13b, whereby each counting unit 13a, 13b counts the number of one of the two or more event signals B1, B2 per time period before the calculating means 13 calculates the mean value MV thereof.

As in the embodiment of fig. 1, the lubrication signal C is in the embodiment of fig. 3 provided for indicating by means of an indicator 15 the need of lubrication of the cutting chain 3.

As in the embodiment of fig. 2, the lubrication signal C is in the embodiment of fig. 4 also provided for triggering, through a line 16 or wirelessly, activation of the pump 7 for feeding a lubricating fluid towards at least one point along the assembly of the cutting chain 3 and the guide bar 2 or activation of the valve for opening and closing the feeding of lubricating fluid to said pump 7.

A combination of the embodiments according to fig. 1 and 2 and fig. 3 and 4 respectively, is also possible.

It should be noted that the above-mentioned time period (gating time) during which the number of event signals B; B1, B2 are counted and after which the calculating means 13 or the counting units 13a, 13b thereof is/are reset, is in the illustrated embodiments set to one second, but may of course vary as required for achieving the best possible result. A suitable gating time may typically be between 10 milliseconds and 2 seconds. The predetermined number of event signals B; B1, B2 required for providing the lubrication signal C may also vary as required and in view of the setting of the time period during which counting is performed. Thus, the event signal reference rate may during normal lubrication be set to e.g. between 20 and 1000 event signals per time period, such as about 200 event signals per time period (e.g. one second). Different event signal rates may be used for starting and stopping lubrication. By way of example, the signal processing arrangement 10 may be configured to start lubrication at a relatively higher event signal reference rate, such as 200 events/s, and to stop lubrication at a relatively lower event signal reference rate, such as 150 events/s. As an alternative, it is possible to count the number of event signals B; B1, B2 per time period during lubrication and if the number is constant, this indicates that lubrication is performed without problems. Then, lubrication is interrupted and restarted after a certain time period or when the event signals rate has increased by a certain number relative to the steady-state rate.

Lubrication is thereafter performed until the number of event signals B; B1, B2 per time period once again is constant.

Still alternatively, the speed of the lubrication pump, or the valve aperture size, may be variably set in proportion to the event signal rate, such that a high event signal rate triggers a high lubricant flow, whereas a low signal rate triggers a low lubricant flow.

The time for performing lubrication may vary. Normally, it takes about 5 to 10 seconds to bring down the number of event signals B; B1, B2 per time period, i.e. the event signal rate, below the event signal reference rate, but lubrication is under all circumstances performed until this is achieved. Accordingly, when the number of event signals B per time period or the mean value MV of the event signals B1, B2 per time period has decreased below the reference number per time period thereof, a lubrication signal C is no longer provided for indicating the need of lubrication of the cutting chain 3 and the indicator 15 may indicate that lubrication can be interrupted, or a lubrication signal C is no longer provided for triggering activation of the pump 7 or of the valve in connection therewith and the operation of the pump 7 or the valve is automatically interrupted.

Similarly as when using the number of event signals B; B1, B2 per time period or a mean value thereof, it is possible to instead use the number of event signals per chain travel distance unit, or a mean value thereof, for the same purpose, i.e. for providing a lubrication signal C for indicating by means of an indicator 15 the need of lubrication of the cutting chain 3 and/or for triggering activation of the pump 7 for feeding a lubricating fluid towards at least one point along the assembly of the cutting chain 3 and the guide bar 2 or for triggering activation of the valve for opening and closing the feeding of lubricating fluid to said pump 7.

In an embodiment schematically illustrated in fig. 5, the signal processing arrangement 10 may comprise an indicator 15 of any suitable type. The signal processing arrangement 10 may process the at least one noise signal A from an acoustic sensor 9a of the sensor arrangement 9 into a signal C1 for indicating the need of lubrication of the cutting chain 3 in response to said noise signal. This indicator 15 as well as the indicator 15 in the embodiments of fig. 1 and 3, may e.g. comprise an LED (light emitting diode), turning said noise signal A into light. The indicator 15 is in the illustrated embodiment of fig. 5 operatively connected to the sensor arrangement 9 by means of an electric lead 17, but the connection may also be wireless.

It should be noted that the friction between the cutting chain members and between the cutting chain 3 and the guide bar 2 and members thereof is affected by several different parameters. Accordingly, the friction increases e.g. when the chainsaw is in use and the speed of the cutting chain 3 is relatively high. With the increased friction, the noise generated thereby is increased and so is the number of event signals B; B1, B2 provided each time a noise signal A; A1, A2 exceeds the reference value thereof, indicating a reference noise level. The RPM of the drive motor or the speed of the cutting chain 3 may be used in an algorithm for optimizing lubrication when lubrication is required.

The tension of the cutting chain 3 also affects the friction between the cutting chain members and between the cutting chain 3 and the guide bar 2 as well as the members of the guide bar. The friction increases with the tension and thus, the noise generated by the friction. The increased noise increases the rate of event signals B; B1, B2 caused thereby and thus, indicates that lubrication is needed.

The increased rate of event signals B; B1, B2 per time period or per chain travel distance unit and thus, the increased friction, may therefore also be used in an application for indicating a possible need for adjustment of the cutting chain. If the need of lubrication has been detected, for example as described above, and lubrication has been performed by manually or automatically activating the pump 7 or pump valve without sensing a sufficient reduction of the friction, e.g. by not having sensed a sufficient reduction of the number of event signals B; B1, B2 per time period or per chain travel distance unit and consequently, without sensing a reduction of the number of lubrication signals C, this is an indication of that the tension of the cutting chain 3 may be too high. Thus, the detection arrangement 8 and the signal processing arrangement 10 of the invention can contribute to indicating the need for controlling and, if required, adjusting the tension of the cutting chain 3. The absence of an expected reduction in friction, despite lubrication, may also be used as an “oil tank empty” indication, or as a general error indication, which may be communicated to the user or trigger a temporary disabling of the chainsaw.

Friction measurements using the detection and signal processing arrangements 8, 10 described hereinabove may be triggered during chain acceleration, for example when one or several predetermined RPM-values are passed. The friction measurements can continue during a predetermined time, or until another RPM value is reached, or both. Friction values obtained at certain RPMs, and/or during certain running conditions, may be given different weights, such as 0 (discarded), 1, or any value therebetween, when used as a basis for determining whether there is a need for lubrication. According to an embodiment, friction values obtained during free-running of the chainsaw, i.e. when the cutting chain does not engage with an object to be cut, may be given a higher weight than friction values obtained when the chainsaw is under load, i.e. during cutting. For example, the signal processing arrangement 10 may be configured to determine any need for lubrication based on acoustic noise signals A obtained when the drive motor 6 operates at a maximum speed, which maximum speed may be determined by a controller controlling the drive motor 6.

Fig. 6 schematically illustrates an alternative method of determining a running condition of the chainsaw, which alternative method may be used for weighting friction values, or for triggering friction measurements. The method makes use of a detection arrangement 8 as described hereinabove, configured to detect a rate R of event signals B (Fig. 1), for example per unit time. The chart illustrates the RPM of the drive motor 6 and the event signal rate R determined by the signal processing arrangement 10 in a scenario where the motor 6 is accelerated under a free-running condition, and thereafter loaded at a point ti in time by bringing the chain 3 into engagement with an object to be cut. Prior to time ti, the event signal rate follows the RPM, whereas at time ti, the RPM decreases while the friction, represented by the rate R, increases. The detection of a signal behaviour corresponding to that illustrated at ti (when derivatives of R and RPM get opposite signs) may be used as an indicator that the chainsaw is no longer free-running. According to an example, the chainsaw may be configured to determine whether there is a need for lubricating the chain based on the acoustic noise signal A (fig. 1) or event signal rate R0at a time to whenever the RPM passes a reference RPM value RPM0, using the methods described hereinbefore. The measured friction may be given the weight 0 or 1 based on whether an engagement with the object to be cut has been detected, such that any values of the friction under load will be discarded (weight=0). When the chainsaw disengages from the object to be cut at t2, the derivatives of R and RPM again get the same signs, any measured friction values may again be given the weight 1.

As a final observation, it should be added that the signal processing arrangement 10, including any comparing means 11 and calculating means 13 as the case may be, may be implemented in any suitable analogue or digital electronics, such as a digital signal processor (DSP), application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), or the like.

It will be evident to a skilled person that the chainsaw according to the present invention can be modified and altered within the scope of the subsequent claims without departing from the idea and purpose of the invention. Thus, as stated, the number, design and location of the acoustic sensors defining the sensor arrangement may vary as required for the respective intended application thereof. The comparing means may be modified to receive, compare and transmit any number of noise and event signals respectively. The calculating means may be modified to receive any number of event signals. As already indicated above, the signal processing arrangement/calculating means can be configured to provide a lubrication signal which can be used for indicating the need of lubrication of the cutting chain as well as for triggering activation of a pump or of a valve for a pump for feeding a lubricating fluid towards at least one point along the assembly of the cutting chain and the guide bar.

Claims

1. A chainsaw comprising a guide bar (2); an endless cutting chain (3) which is mounted so as to turn around the guide bar (2); a drive motor (6) for driving the cutting chain (3); a detection arrangement (8) configured to detect the need of lubrication of the cutting chain (3); and a signal processing arrangement (10) for processing information from the detection arrangement (8), the chainsaw being characterized in that said detection arrangement (8) comprises a sensor arrangement (9) comprising a first acoustic sensor (9a; 9b; 9c), the sensor arrangement (9) being configured to sense a friction relating to the cutting chain (3) and the guide bar (2) by measuring an acoustic noise generated by said friction when said cutting chain is operated to turn around said guide bar.

2. The chainsaw according to claim 1, wherein said first acoustic sensor (9a; 9b; 9c) is configured to resonate at an acoustic noise frequency of said friction.

3. The chainsaw according to any of the previous claims, wherein said first acoustic sensor (9a; 9b, 9c) is configured to resonate at an ultrasonic resonance frequency, e.g. between 20 and 1000 KHz; preferably, more than 50 kHz; and more preferably, between 100 and 500 KHz.

4. The chainsaw according to any of the previous claims, wherein said first acoustic sensor (9a; 9b, 9c) is a piezoelectric sensor.

5. The chainsaw according to any of the previous claims, wherein the detection arrangement (8) is mounted on the chainsaw in physical contact with the guide bar (2), or directly on the guide bar (2).

6. The chainsaw according to any of the previous claims, wherein said sensor arrangement (9) is configured to provide a first noise signal (A; A1, A2), indicative of the noise generated by the friction relating to the cutting chain (3) and the guide bar (2), to the signal processing arrangement (10).

7. The chainsaw according claim 6, wherein said sensor arrangement (9) comprises a second acoustic sensor (9a; 9b; 9c) configured to measure the acoustic noise generated by the friction relating to the cutting chain (3) and the guide bar (2), wherein said second sensor (9a; 9b; 9c) is configured to provide a second noise signal (A1 ; A2) indicative thereof.

8. The chainsaw according to claim 7, wherein said first and second acoustic sensors (9a; 9b; 9c) have different resonance frequencies.

9. The chainsaw according to any of the claims 6-8, wherein said signal processing arrangement (10) is configured to compare said first noise signal (A; A1, A2) with a noise signal reference value, and provide an event signal (B; B1, B2) based on said noise signal exceeding said noise signal reference value.

10. The chainsaw according to claim 9, wherein the signal processing arrangement (10) is configured to determine a rate of event signals (B; B1, B2) and generate a lubrication signal (C) based on the event signal rate exceeding an event signal reference rate.

11. The chainsaw according to any of the previous claims, wherein said signal processing arrangement (10) is configured to generate a lubrication signal based on an RPM of the drive motor (6).

12. The chainsaw according to any of the previous claims, further comprising an indicator (15) which is operatively connected to the sensor arrangement (9) and configured for indicating, to a user, the need of lubrication of the cutting chain (3) in response to said noise signal (A).

13. The chainsaw according to any of the previous claims, wherein said signal processing arrangement (10) is configured to, based on a detected change or lack of change of friction following a lubrication, indicate a possible need for adjustment of the tension of the cutting chain.

14. A method for detecting the need of lubrication of a cutting chain (3) of a chainsaw, the method comprising, operating the cutting chain (3) to turn about a guide bar (2); measuring an acoustic noise generated by friction when said cutting chain (3) is operated to turn around said guide bar (2); and based on the measured acoustic noise, generating a first noise signal (A; A1, A2).

15. The method according to claim 14, wherein measuring the acoustic noise comprises measuring the acoustic noise at an ultrasonic frequency, for example of between 20 and 1000 KHz; preferably, more than 50 kHz; and more preferably, between 100 and 500 KHz.

16. The method according to any of the claims 14-15, wherein said sensor arrangement (9) is configured to provide a first noise signal (A; A1, A2), indicative of the noise generated by the friction relating to the cutting chain (3) and the guide bar (2), to a signal processing arrangement (10).

17. The method according any of the claims 14-16, wherein measuring the acoustic noise comprises measuring the acoustic noise at two spatially separated positions.

18. The method according any of the claims 14-17, wherein measuring the acoustic noise comprises measuring the acoustic noise at two separate frequencies.

19. The method according to any of the claims 14-18, further comprising comparing said first noise signal (A; A1, A2) with a noise signal reference value and, based on the noise signal exceeding said noise signal reference value, generating at least one event signal (B; B1, B2).

20. The method according to claim 19, wherein said method further comprises counting a rate of event signals (B; B1, B2) and, based on the event signal rate exceeding an event signal reference rate, generating a lubrication signal (C)

21. The method according to any of the claims 14-20, comprising determining whether the chainsaw is free-running; and based on said determination, determining whether there is a need for lubrication of the cutting chain (3).

22. The method according to any of the claims 14-21, further comprising indicating, to a user, the need of lubrication of the cutting chain (3).

23. The method according to any one of claims 14-22, further comprising, based on a detected change or lack of change of friction following a lubrication, indicating a possible need for adjustment of the tension of the cutting chain (3).

24. Use of the detection arrangement (8) and the signal processing arrangement (10) of the chainsaw according to any one of claims 1-13 for indicating, following a lubrication, a possible need for adjustment of the tension of the cutting chain (3).