Cutting system, method, and trained classifier

Abstract

A cutting system comprises a handheld power cutter having a power head with a drive motor, and a cutting chain assembly comprising a cutting chain drive sprocket configured to be rotated by the drive motor about a drive sprocket axis, a guide bar extending from the power head, and a cutting chain guided along the guide bar. The cutting system further comprises a magnetic detection assembly (36) comprising at least one magnetic field sensor (36a-36f) configured to detect a magnetic field perturbation generated by the cutting chain assembly; and data processing equipment (42) configured to receive sensor data from the magnetic detection assembly (36); and determine, based on a detected magnetic field perturbation, at least one structural condition of the cutting chain assembly.

Description

[0001] CUTTING SYSTEM, METHOD, AND TRAINED CLASSIFIER

[0002] Field of the invention

[0003] The present invention relates to a cutting system comprising a handheld power cutter, to a method of determining a structural condition of such a handheld power cutter, and to a trained classifier trained to determine such a structural condition.

[0004] Chainsaws have been known for the last 100 years or so. Chainsaws, as well as certain other types of handheld power cutters, have a cutting chain assembly comprising a cutting chain guided along an elongate guide bar, and a cutting chain drive sprocket driving the cutting chain along the periphery of the guide bar. Such power cutters need to be regularly serviced and maintained to, for example, sharpen cutting teeth, replace worn parts, and adjust chain tension. It is an object of the present invention to make such handheld power cutters easier to operate, service and maintain.

[0005] It is an object of the present invention to solve, or at least mitigate, parts or all of the above-mentioned problems. To this end, there is provided a cutting system comprising a handheld power cutter, the handheld power cutter comprising a power head comprising a drive motor; and a cutting chain assembly comprising a cutting chain drive sprocket configured to be rotated by the drive motor about a drive sprocket axis, a guide bar extending from the power head, and a cutting chain guided along the guide bar, wherein the cutting system comprises a magnetic detection assembly comprising at least one magnetic field sensor configured to detect a magnetic field perturbation generated by the cutting chain assembly; and data processing equipment configured to receive sensor data from the magnetic detection assembly; and determine, based on a detected magnetic field perturbation, at least one structural condition of the cutting chain assembly. The data processing equipment may be arranged in the power cutter itself. Alternatively, the data processing equipment may be comprised in another device separate from the power cutter, and configured to receive sensor data from the magnetic detection assembly via e.g. a cable or a wireless data link. Similarly, the at least one magnetic field sensor may comprise one or more magnetic field sensors comprised in the power cutter. For example, the at least one magnetic field sensor may comprise one or more magnetic field sensors attached to the handheld power cutter, for example to the power head and / or to the guide bar. Alternatively or additionally, the at least one magnetic field sensor may comprise one or more magnetic field sensors comprised in a device separate from the power cutter, such as a in a glove. The cutting chain may be a saw chain, and accordingly, the power cutter may be a chainsaw. The drive motor may be an internal combustion engine or an electric motor, which may be battery powered. An electric motor may result in an improved detection accuracy due to the cleaner magnetic environment around an electric motor, compared to that generated by an ignition system of an internal combustion engine. The power head may comprise a set of handles for holding the power head with two hands. The at least one magnetic field sensor may comprise one magnetic field sensor, or a plurality of magnetic field sensors. The structural condition of the cutting chain assembly may comprise, for example, a magnetic fingerprint of a shape of a component of the cutting chain assembly, such as the shape of the cutting chain drive sprocket, or the shape of a pattern embossed in any part of the cutting chain assembly, whereby the type or model of said component can be identified. The sensor data may be sampled as a function of time, and any changes of the determined structural condition may be indicative of a change of e.g. a state of wear of components of the cutting chain assembly.

[0006] According to embodiments, said data processing equipment may be configured to determine said at least one structural condition of the cutting chain assembly based on a detected magnetic field perturbation frequency pattern. Due to the cyclic nature of the motion of parts of the cutting chain assembly, structural conditions of moving parts of the cutting chain assembly will appear as periodic variations in the detected magnetic field perturbation.

[0007] According to embodiments, said data processing equipment may further be configured to receive said sensor data from the magnetic detection assembly as time-variant sensor data; and convert said time-variant sensor data to frequency domain. Due to the cyclic nature of the motion of parts of the cutting chain assembly, representation in frequency domain enables improved detection of changes of structural conditions of the cutting chain assembly. The time-variant sensor data may be converted to frequency domain using for example a discrete Fourier transform (DFT) or a fast Fourier transform (FFT) algorithm.

[0008] According to embodiments, said data processing equipment may further be configured to identify, based on frequency data obtained by said conversion, a magnitude at each of one or more frequency bins associated with a respective magnetic field perturbation frequency. For example, a magnitude at a frequency corresponding to the rate at which cutting teeth of the cutting chain pass the sensor may be indicative of a state of wear of the cutting teeth. The one or more respective magnetic field perturbation frequencies may be predetermined, or may be dynamically set, e.g. in dependence of an RPM of the drive motor. According to embodiments, at least one respective magnetic field perturbation frequency is lower than 10 MHz, and more preferably, lower than 100 kHz. Alternatively or additionally, at least one respective magnetic field perturbation frequency may typically exceed 10 Hz, and may even more preferably exceed 20 Hz.

[0009] According to embodiments, said data processing equipment may further be configured to determine a ratio between a magnitude at a first frequency bin associated with a first magnetic field perturbation frequency, and a magnitude at a second reference frequency bin. For example, a ratio between the magnitude at a first frequency corresponding to the rate at which sprocket teeth pass the sensor, and the magnitude at a second reference frequency which is a multiple of the first frequency, may indicate the state of wear of the sprocket.

[0010] According to embodiments, said determination of at least one structural condition of the cutting chain assembly may further be based on a determined RPM, i.e. number of revolutions per minute, of the drive motor. The RPM may be received from a motor controller or determined by measuring a rotation speed of e.g. a drive motor shaft. Alternatively, the magnetic detection assembly may be configured to sample sensor data only at specific RPMs of the motor. By comparing a detected magnetic field perturbation frequency pattern with the RPM, elements appearing as a multiple of the RPM, such as the number of teeth of the drive sprocket, may conveniently be identified in the detected magnetic field perturbation frequency pattern. Moreover, the signal may be band-pass filtered with a pass-band positioned at the RPM or a multiple thereof; thereby, signal elements resulting from the shape of e.g. the cutting links may easier be identified and analyzed.

[0011] According to embodiments, said at least one magnetic field sensor may be positioned at a distance from the cutting chain assembly of less than 150 mm. According to further embodiments, the at least one magnetic field sensor may be positioned at a distance from the cutting chain assembly of less than 50 mm. The magnetic detection assembly may comprise a plurality of magnetic field sensors which are positioned at mutually different distances from the cutting chain assembly.

[0012] According to embodiments, said cutting chain drive sprocket may comprise a set of sprocket teeth, a radially outermost tip of which is configured to follow a circular drive sprocket tooth path about the drive sprocket axis, wherein the at least one magnetic field sensor comprises a magnetic field sensor positioned at a distance of less than 50 mm from said drive sprocket tooth path. Such a position is particularly well suited for detecting events relating to the meshing relationship between drive sprocket and cutting chain. For example, a change in magnitude of the magnetic field perturbation may be indicative of the cutting chain “climbing” on the drive sprocket, which may indicate a change in the chain tension. A loose chain increases the risk of a chain jump; accordingly, excessive chain climbing also serves as an indicator of increased risk of chain jump.

[0013] According to embodiments, said guide bar may comprise a nose sprocket meshing with the cutting chain, the nose sprocket comprising a set of nose sprocket teeth, a radially outermost tip of which is configured to follow a circular nose sprocket tooth path about a nose sprocket axis, wherein the at least one magnetic field sensor comprises a magnetic field sensor positioned at a distance of less than 50 mm from said nose sprocket tooth path. Such a position is particularly well suited for detecting events relating to the meshing relationship between nose sprocket and cutting chain. For example, a change in magnitude of the magnetic field perturbation may be indicative of the cutting chain “climbing” on the nose sprocket, which may indicate a change in the chain tension. A loose chain increases the risk of a chain jump; accordingly, excessive chain climbing also serves as an indicator of increased risk of chain jump.

[0014] According to embodiments, said at least one magnetic field sensor may comprise a magnetoresistive sensor, such as a tunnel magnetoresistive sensor, or a fluxgate magnetometer. Thereby, a particularly high sensitivity may be obtained, which enables a high degree of flexibility in the positioning of the magnetic field sensor in relation to the cutting chain assembly, and also enables simultaneous detection of structural conditions of a plurality of spatially separated parts of the cutting chain assembly using a single magnetic field sensor. The highly compact dimensions of a magnetic tunnel junction is convenient to integrate at virtually any position, and thereby enables a particularly high degree of flexibility in the positioning of the magnetic field sensor in relation to the cutting chain assembly. This enables a high quality of the captured signal. On the other hand, the low detection limit and high sensitivity and of a fluxgate sensor enables detecting the magnetic field perturbation at a greater distance which, accordingly, also enables a particularly high degree of flexibility in the positioning of the magnetic field sensor in relation to the cutting chain assembly.

[0015] According to embodiments, said at least one magnetic field sensor may comprise a three-dimensional sensor. Thereby, the detection of the magnetic field perturbation may comprise a detection of a perturbation of the direction of a magnetic field vector. Alternatively or additionally, the detection of the magnetic field perturbation may comprise a detection of a perturbation of the magnitude of a magnetic field vector. The three-dimensional sensor may be configured to detect a magnetic field perturbation generated by the cutting chain assembly along each of three mutually orthogonal axes. According to embodiments, the data processing equipment may be configured to determine said at least one structural condition of the cutting chain assembly based on a relationship between magnetic field perturbations along mutually orthogonal axes.

[0016] According to embodiments, said at least one magnetic field sensor may comprise at least one magnetic field sensor positioned in a plane defined by the guide bar. Such a position may be particularly beneficial for detecting a magnetic field perturbation generated by e.g. a cutting edge of the cutting chain, or by the drive teeth of a cutting chain drive sprocket of rim type. Said at least one magnetic field sensor positioned in a plane defined by the guide bar may, for example, comprise a magnetic field sensor attached to the guide bar; alternatively or additionally, said at least one magnetic field sensor positioned in a plane defined by the guide bar may comprise a magnetic field sensor attached to the power head.

[0017] According to embodiments, said at least one magnetic field sensor may comprise a magnetic field sensor positioned outside a plane defined by the guide bar. Such a position may be particularly beneficial for detecting the magnetic field perturbation at a short detection distance between the at magnetic field sensor and the cutting chain without risking damage to the magnetic field sensor. This is useful for detecting, for example, the magnetic field perturbation generated by comparatively small elements, such as the shape of a cutting edge or the sharpness of a cutting edge. It may also be beneficial for protecting the at least one sensor against build-up of dirt, and thereby enables detection over extended periods of time. According to embodiments, the at least one magnetic field sensor is positioned in register with the cutting chain. Such a position may be particularly well suited for detecting movement of the cutting chain’s path in the axial direction. Thereby, e.g. a meandering path of the cutting chain, due to e.g. a mismatch between an axial width of the guide track of the guide bar and an axial thickness of drive links of the cutting chain, may be conveniently detected. Such a mismatch may occur by e.g. using a saw chain intended for the 1 ,3 mm-standard track with on a guide bar with a track width following the 1 ,5 mm-standard. A meandering path which develops and increases over time may also indicate a worn guide track of the guide bar. Said at least one magnetic field sensor positioned outside a plane defined by the guide bar may, for example, comprise a magnetic field sensor attached to a lateral surface of the guide bar, for example at a proximal end of the guide bar; alternatively or additionally, said at least one magnetic field sensor positioned outside a plane defined by the guide bar may comprise a magnetic field sensor attached to the power head.

[0018] According to embodiments, said data processing equipment may be configured to store data samples captured by said at least one magnetic field sensor at a sampling rate exceeding 100 Hz. Preferably, the sampling rate exceeds 1 kHz.

[0019] According to embodiments, said data processing equipment may further be configured to, based on said determination of at least one structural condition of the cutting chain assembly, automatically stop the cutting chain sprocket. For example, the data processing equipment may generate a signal based on a determination that the cutting chain has climbed on the drive sprocket and thereby risks jumping.

[0020] According to embodiments, said data processing equipment may further be configured to, based on said determination of at least one structural condition of the cutting chain assembly, generate an alert signal to a user of said cutting system. For example, the data processing equipment may generate a signal based on a determination that an element of the cutting chain assembly, such as a cutting chain, is worn. The alert signal may be generated e.g. as a light alert, a sound alert, and / or an icon or other message on a display. The alert signal may be generated by the by the handheld power cutter, or by any other device, such as headphones or a mobile phone, which may be in communication with the magnetic detection assembly.

[0021] According to embodiments, the magnetic detection assembly may further comprise at least one magnet configured to generate a baseline magnetic field across at least a portion of said cutting chain assembly, and the at least one magnetic field sensor is configured to detect a perturbation, generated by the cutting chain assembly, of the baseline magnetic field. The at least one magnet may comprise a permanent magnet and / or an electromagnet. The latter may be less prone to demagnetization over time, which ascertains a reliable detection over extended periods of time. The at least one magnet may be arranged separate from the cutting chain assembly. The at least one magnet may be configured to generate a baseline magnetic field, across said at least a portion of said cutting chain assembly, exceeding 1 ,0 pT, or optionally, even exceeding 10 pT. Thereby, any contribution of the geomagnetic field to the baseline magnetic field may be safely disregarded, such that the spatial orientation of the power cutter will not affect measurements. Alternatively, the magnetic detection assembly may be free from any magnet generating a baseline magnetic field. Thereby, instead, the at least one magnetic field sensor will detect a perturbation, generated by the cutting chain assembly, of the geomagnetic field. Still alternatively, the cutting chain assembly may be at least partly magnetized to create its own persistent magnetic field. A persistent magnetic field of the cutting chain assembly may be automatically detected e.g. using a reference sensor remote from the cutting chain assembly, which remote sensor detects the direction of the earth magnetic field direction. Alternatively, a persistent magnetic field of any component of the cutting chain assembly may be detected by determining the amplitude ratio of the magnetic perturbation generated by one component, for example the cutting chain, to the magnetic perturbation generated by another component, for example the sprocket.

[0022] According to embodiments, the magnetic detection assembly may be a passive magnetic detection assembly. Herein, a passive magnetic detection assembly is construed as the opposite to an active magnetic detection assembly, i.e. a magnetic detection assembly which modulates and emits a magnetic field, and detects the changes in the return signal. Accordingly, a passive magnetic detection assembly does not emit a modulated magnetic field, but instead detects only a modulation of the magnetic field which originates from the cutting chain assembly itself.

[0023] According to embodiments, said data processing equipment may comprise a trained classifier configured to determine, based on the detected magnetic field perturbation, said at least one structural condition of the cutting chain assembly. For example, the determination may be based on a detected magnetic field perturbation frequency pattern, which may be represented in the frequency domain.

[0024] According to embodiments, said at least one structural condition of the cutting chain assembly comprises at least one of a state of wear of the cutting chain, a state of wear of the drive sprocket, a state of wear of the guide bar, a cutting chain type, a drive sprocket type, and a cutting chain tension. For example, the high-frequency content of dynamically captured magnetic signature enables determining the sharpness of a moving cutting chain. The detection of a flexing of the cutting chain within the guide bar plane may indicate a slacked cutting chain, which may be indicative of wear or an improperly tensioned chain.

[0025] According to embodiments, the cutting system may comprise at least one magnetic field sensor configured to detect a deflection of the cutting chain in a direction perpendicular to a longitudinal axis of the guide bar, along a plane defined by the guide bar, wherein said at least one structural condition of the cutting chain assembly comprises a cutting chain tension.

[0026] According to a second aspect, there is provided a trained classifier trained to determine, based on a detected magnetic field perturbation from a magnetic detection assembly, at least one structural condition of a cutting chain assembly of a handheld power cutter.

[0027] According to a third aspect, there is provided a method of determining a structural condition of cutting chain assembly of a handheld power cutter, comprising: receiving time-variant sensor data from a magnetic detection assembly; converting said time-variant sensor data to frequency domain to obtain a magnitude at each of one or more frequency bins associated with a respective magnetic field perturbation frequency; and, based on the one or more respective magnetic field perturbation frequencies and a reference frequency pattern, recognizing said structural condition. The reference frequency pattern may be a predetermined pattern which may be recognized in the frequency-domain data. The handheld power cutter may be the handheld power cutter of a cutting system as defined above.

[0028] According to embodiments, the method may comprise determining a ratio between a magnitude at a first frequency bin associated with a first magnetic field perturbation frequency, and a magnitude at a second reference frequency bin.

[0029] It is noted that embodiments of the invention may be embodied by all possible combinations of features recited in the claims, as well as of the further embodiments defined hereinabove. Moreover, the trained classifier according to the second aspect, as well as the method according to the third aspect, may each be combined with any of the embodiments of the cutting system according to the first aspect.

[0030] Brief description of the drawings

[0031] The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and nonlimiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein:

[0032] Fig. 1 is a plan view of a cutting system comprising a handheld power cutter embodied as a chainsaw, and a device external to the handheld power cutter embodied as a mobile phone;

[0033] Fig. 2 is a perspective view of the chainsaw of Fig. 1 with a chain sprocket cover removed to expose a cutting chain drive sprocket of the chainsaw;

[0034] Fig. 3 is a magnified side view of an interface between a saw chain, a saw chain drive sprocket, and a guide bar of the chainsaw of Fig. 1 ;

[0035] Fig. 4 is a section of the cutting chain and a portion of the guide bar of Fig. 3, the section taken along the line IV-IV of Fig. 3;

[0036] Fig. 5 is a section of the cutting chain and guide bar of the chainsaw of Fig. 1 at a distal end of the guide bar, the section taken along a centre plane of the guide bar;

[0037] Fig. 6 is a schematic illustration of functional blocks of control electronics of the chainsaw of Fig. 1 , and in particular, data processing equipment configured to process sensor data received from a magnetic detection assembly of the cutting system of Fig. 1 , along with the mobile phone of Fig. 1 ;

[0038] Fig. 7 is a schematic illustration of data received from the magnetic detection assembly of the chainsaw of Fig. 1 , the data being represented in time domain as well as in frequency domain;

[0039] Fig. 8A is a first spectrogram illustrating frequency-domain data received from the magnetic detection assembly of the chainsaw of Fig. 1 ;

[0040] Fig. 8B is a second spectrogram illustrating frequency-domain data received from the magnetic detection assembly of the chainsaw of Fig. 1 ;

[0041] Fig. 9A is a perspective view of the cutting chain drive sprocket of Fig. 2 prior to being exposed to wear; Fig. 9B is a perspective view of the cutting chain drive sprocket of Fig. 2 after being exposed to wear;

[0042] Fig. 10 is a perspective view of an alternative embodiment of a cutting chain drive sprocket for the chainsaw of Fig. 2;

[0043] Fig. 11 is a flow chart illustrating a method of determining a structural condition of cutting chain assembly of a handheld power cutter; and

[0044] Fig. 12 is a perspective view of a CD-ROM.

[0045] All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the embodiments, wherein other parts may be omitted.

[0046] Detailed description of the exemplary embodiments

[0047] Fig. 1 illustrates a cutting system 8 comprising handheld power cutter embodied as a handheld chainsaw 10. The chainsaw 10 comprises a power head 12 provided with a pair of handles 14a, 14b, by means of which an operator (not illustrated) may hold and operate the chainsaw 10. The pair of handles comprises a front handle 14a, typically for holding with the left hand, and a rear handle 14b, typically for holding with the right hand. A cutting chain assembly 15 comprising a cutting chain 16, and an elongate guide bar 18 guiding the cutting chain 16 in an elongate loop, extends from a front end of the chainsaw body 12 along a longitudinal axis X of the chainsaw 10, which longitudinal axis X is defined by the longitudinal centre axis of the guide bar 18. A vertical axis Y of the chainsaw, perpendicular to the longitudinal axis X, is also defined by the extension plane of the guide bar 18. The illustrated cutting chain 16 comprises cutting teeth configured to shave off wood chips from a work piece, such as a piece of timber; accordingly, the cutting chain 16 is of saw chain type. The chainsaw 10 further comprises a removable battery 20 in a battery compartment 20a, an electric drive motor 22 (only schematically indicated by a broken-line circle in Fig. 1 ) powered by the battery 20, and a finger-operated trigger 24 permitting the operator to selectively mobilize the cutting chain 16 using the electric motor 22. The trigger 24 extends downwards from a bottom face of the rear handle 14b, and is movable between a depressed position (not illustrated), responsive to which the electric motor 22 is operated to move the cutting chain 16, and a released position (illustrated), responsive to which the cutting chain 16 is stopped. Control electronics 25, schematically illustrated by a broken-line rectangle, comprises electronics configured to control the operation of the chainsaw based on operator input received from e.g. the trigger 24. The cutting system 8 further comprises an optional electronics device 11 external to the chainsaw 10 and in communication with the chainsaw 10; in the illustrated embodiment the device 11 external to the chainsaw is a portable user terminal, embodied as a mobile phone 13.

[0048] Fig. 2 illustrates the chainsaw 10 without the cutting chain 16 (Fig. 1 ), and with a chain sprocket cover 26 (Fig. 1 ) removed to expose the attachment of the guide bar 18 to the chainsaw body 12. As apparent in Fig. 2, the cutting chain assembly 15 further comprises a cutting chain drive sprocket 28 configured to be rotated by the drive motor 22 about a drive sprocket axis A1. The guide bar comprises a nose sprocket (not visible in Fig. 2) which rotates about a nose sprocket axis A2, parallel to the drive sprocket axis A1 .

[0049] Fig. 3 schematically illustrates the cutting chain drive sprocket 28, a short section of the cutting chain 16, and a proximal end of the guide bar 18, in a section taken along a plane L defined by a lateral face of the guide bar 18. The cutting chain drive sprocket 28 is rotated by the motor 22 (Fig. 1 ), and drivingly engages with the cutting chain 16 to move the cutting chain 16 along the guide bar 18. The cutting chain 16 comprises drive links 16a meshing with drive sprocket teeth 30 of the cutting chain drive sprocket 28. Radially outermost tips 30a of the drive sprocket teeth 30 follow a circular path P1 about the drive sprocket rotation axis A1 . Cutter links 16b and tie straps 16c hold the drive links 16a together.

[0050] Fig. 4 is an illustration of a section of the cutting chain 16 and guide bar 18 along the line IV-IV of Fig. 3. The drive links 16a are pivotally connected to the cutter links 16b and tie straps 16c by rivets 15. Each cutter link 16b is provided with a cutting tooth 17 adapted to shave off wood chips from the material being cut, and a depth gauge 19 which limits the thickness of the wood chip shaved off the material being cut. Bottom edges of the cutter links 16b and tie straps 16c ride on the guide bar 18, and lower ends of the drive links 16a are guided within a guide track 18a of the guide bar. The lateral width G of the guide track 18a, perpendicular to the XY plane (Fig. 1 ) of the guide bar 18, matches the corresponding width of the drive links so as to guide the cutting chain 16 along the centre plane XY (Fig. 1) of the guide bar 18.

[0051] Fig. 5 is a section along the XY plane (Fig. 4) of a distal end of the guide bar 18, opposite to the guide bar’s 18 proximal end attached to the power head 12 (Fig. 1). The distal end of the guide bar 18 comprises the nose sprocket 34, which is provided with a set of nose sprocket teeth 34a meshing with the cutting chain 16. Radially outermost tips 34b of the nose sprocket teeth 34a follow circular nose sprocket tooth path P2 about the nose sprocket axis A2 (Fig. 2).

[0052] The cutting system 8 (Fig. 1 ) further comprises a magnetic detection assembly 36 comprising a first magnetic field sensor 36a positioned at the distal end of the guide bar 18, adjacent to the nose sprocket 34. The first magnetic field sensor 36a is comprised within the guide bar 18, in the centre plane XY of the guide bar.

[0053] Returning to Fig. 2, the magnetic detection assembly 36 further comprises a second magnetic field sensor 36b on the power head 12 behind the chain sprocket cover 26 (Fig. 1 ), and a third magnetic field sensor 36c positioned on a glove 32 worn by an operator of the chainsaw 10 or on any other places on the operators body.

[0054] As illustrated in Fig. 3, the magnetic detection assembly 36 further comprises a fourth magnetic field sensor 36d positioned on a proximal end of the guide bar 18, and a fifth magnetic field sensor 36e positioned on the power head, in the XY plane (Fig. 1 ), facing a position on the cutting chain drive sprocket 28 where the cutting chain 16 meshes with the cutting chain drive sprocket 28.

[0055] Fig. 4 illustrates a sixth magnetic field sensor 36f attached to the power head 12 (Fig. 1 ) outside the XY plane defined by the guide bar 18. The first, second, fourth and fifth magnetic field sensors 36a, 36b, 36d, 36e are positioned within the XY plane of the guide bar 18, whereas the third and sixth magnetic field sensors 36c, 36f are outside the XY plane. The sixth magnetic field sensor 36f is laterally offset from the cutting chain 16 in an offset direction perpendicular to the XY plane, but otherwise in register with the cutting teeth’s 17 path along the guide bar 18.

[0056] Each of the respective magnetic field sensors 36a-36f is positioned either directly on the cutting chain assembly 15, or at a distance therefrom of less than 150 mm. The first, second, fourth, fifth and sixth magnetic field sensors 36a, 36b, 36d, 36e and 36f are tunnel magnetoresistive sensors, which are positioned at a distance from the cutting chain assembly 15 of less than 50 mm, whereas the third magnetic field sensor 36c is a fluxgate magnetometer. It will however be appreciated that any of the magnetic field sensors 36a-f may be of either of the mentioned types, or of any other type. The second and fifth magnetic field sensors 36b, 36e (Fig. 3) are also positioned at a distance of less than 50 mm from the drive sprocket tooth path P1 , and the first magnetic field sensor 36a is positioned at a distance of less than 50 mm from the nose sprocket tooth path P2. Such positions in relation to the respective sprockets 28, 34 are particularly well suited for detecting events relating to the meshing relationship between the cutting chain 16 and the respective sprockets 28, 34, as will be explained further below.

[0057] Fig. 6 schematically illustrates functional blocks of the control electronics 25 (Fig. 1 ). The control electronics 25 comprises a motor controller 40 controlling the drive motor 22 based on input from the trigger 24, and data processing equipment 42 configured to receive sensor data from the magnetic detection assembly 36. The data processing equipment 42 may comprise e.g. one or more sample and hold circuits 42a, one or more analogue-to-digital converters 42b, and one or more microprocessors 42c. The one or more microprocessors 42c may comprise a digital signal processor, DSP. The data processing equipment 42 may further comprise computer memory 42d loaded with instructions for processing sensor data received from the magnetic detection assembly 36, and / or computer memory 42e configured to store processed and / or unprocessed data received from the magnetic detection assembly 36. The data processing equipment 42 may be configured to receive RPM information from the motor controller 40; alternatively, the RPM may be measured directly on the drive motor 22. The control electronics 25 further comprises a wireless transceiver 43 configured to communicate with the electronics device 11 external to the chainsaw 10.

[0058] The data processing equipment 42 is configured to sample the respective magnetic fields detected by each of the magnetic field sensors 36a-e (Figs 2-4) at regular intervals. By comparing the detected magnetic fields to baseline magnetic field(s), which for example may be represented by the background geomagnetic field and / or a static magnetic field applied by e.g. a permanent magnet 44 (Fig. 3), the data processing equipment 42 detects the occurrence of any perturbation of the magnetic field generated by the cutting chain assembly 15 within the detection range of the respective magnetic field sensors 36a-f. Thereby, various structural conditions of the cutting chain assembly 15 may be determined. The sensor data is sampled as a function of time, and preferably, at a regular sampling rate; for example, the respective magnetic field sensors 36a-f may be sampled at a sampling rate of about 10 kHz.

[0059] Referring to Fig. 7, for each respective magnetic field sensor 36a-f, consecutive samples Si , S2...Sn are sampled in each of a series of finite, consecutive sampling windows Wi, W2... For example, each sampling window W1, W2... may comprise 1000 samples (i.e. n=1000), such that, with a sampling rate of 10 kHz, each sampling window W1, W2... covers a time span of 1 / 10 second. The sensor data S-i-Sn obtained during each respective finite sampling window Wi, W2... is converted by the data processing equipment 42 to frequency domain via a discrete Fourier transform. This results in a sequence or feed of discrete Fourier transforms DFT1, DFT2..., each discrete Fourier transform being a frequency domain representation of the time-variant sensor data S-i-Sn sampled during a respective sampling window W1, W2..., each respective discrete Fourier transform DFT1, DFT2... representing the frequency content magnitudes at each of a series of frequency bins Bi, B2...Bn. As such, each respective discrete Fourier transform DFT1, DFT2... defines a magnetic field perturbation frequency pattern.

[0060] Fig. 8A illustrates a first sequence of discrete Fourier transforms DFT1, - DFTm generated based on a respective sequence of sampling windows, each sampling window comprising a set of consecutive samples S-i-Sn captured from the fourth sensor 36d (Fig. 3). In Fig. 8A, the data is represented in the form of a spectrogram 50a, wherein the x-axis represents frequency, the y-axis represents time, i.e. the consecutive order of discrete Fourier transforms DFT1, DFT2, ... DFTm, and the degree of blackness represents the amplitude or magnitude at each respective frequency bin Bi, B2...Bn(Fig. 6). The spectrogram 50a of Fig. 8A was captured while running the chainsaw 10 (Fig. 1 ) at a constant, known RPM, using a spur-type cutting chain drive sprocket 28 provided with seven drive sprocket teeth 30 (Fig. 3).

[0061] Fig. 8B illustrates a spectrogram 50b generated in the same manner as that of Fig. 8A, at the same constant RPM, the difference being that the spectrogram 50b of Fig. 8B was captured using a spur-type cutting chain drive sprocket 28 provided with only six drive sprocket teeth 30 (Fig. 3). The differences in the magnetic field perturbation frequency pattern of Fig. 8B, compared to that of Fig. 8A, are caused by the different number of drive sprocket teeth 30 in the two respective cases, and appears as a frequency shift of spectral peaks. Similar spectrograms may be obtained from each of the respective magnetic field sensors 36a-e for detecting various structural conditions of the cutting chain assembly 15 (Fig. 1 ).

[0062] While it may be sufficient to capture only the magnetic field perturbation amplitude in a single magnetic field direction, each of the magnetic field sensors 32a- f is a three-dimensional sensor configured to detect a magnetic field perturbation along three orthogonal detection axes. The use of three-dimensional sensors enables determining the absolute value of the magnitude of the magnetic field perturbation regardless of the orientation of the chainsaw 10 within the baseline magnetic field. Moreover, it also enables detecting magnetic field perturbations generated by the cutting chain assembly 15 (Fig. 1 ) which do not result in a change of magnetic field magnitude, but manifest themselves only in a magnetic field direction change.

[0063] Figs 9A illustrates a new cutting chain drive sprocket 28 of spur type, whereas Fig. 9B illustrates the same cutting chain drive sprocket 28 in a worn condition. The wear manifests itself e.g. as dents 31 in the radially outermost tips 30a of the drive sprocket teeth 30. The dents 31 cause the appearance of new spectral peaks in the spectrogram generated by the data processing equipment 42. By comparing the generated spectrogram with a reference spectrogram, obtained in advance using a cutting chain drive sprocket which has not been exposed to wear, the data processing equipment 42 may identify the occurrence of new spectral peaks representing wear. When the wear of the cutting chain drive sprocket exceeds a limit wear, a signal 46 (Fig. 6) is sent to the device 11 external to the chainsaw 10 (Fig. 1 ), alerting a user of the chainsaw 10 that it is time to replace the cutting chain drive sprocket 28. It will be appreciated that the state of wear of the nose sprocket 34 (Fig. 5) may be determined in a similar manner using the first magnetic field sensor 36a.

[0064] Fig. 10 illustrates a cutting chain drive sprocket 28 of rim type, i.e. comprising, in addition to the cutting chain drive teeth 30, a pair of support rims 29a, 29b configured to radially support the cutter links 16b and tie straps 16c to provide smooth running of the cutting chain 16. Through the recognition of characteristic peaks and their magnitudes in the spectrogram obtained from the magnetic detection assembly 36 (Fig. 2), the data processing equipment 42 may also determine whether the cutting chain drive sprocket 28 is of spur type (Figs 9A, 9B) or of rim type (Fig. 10), which may likewise be communicated to the external device 11 , and thereby facilitate e.g. selection of a replacement sprocket or a new cutting chain in the hardware store. In particular, a rim-type cutting chain drive sprocket (Fig. 10) distinguishes from a spur-type cutting chain drive sprocket (Figs 9A, 9B) in that the rims 29a, 29b generate a large perturbation amplitude at the zero- or low-frequency bins Bi, B2... (Fig. 7), whereas the rims 29a, 29b at the same time to a certain extent magnetically shields the sprocket teeth 30 from generating a perturbation at a frequency corresponding to the frequency at which the sprocket teeth 30 pass the respective magnetic field sensor 36d. Accordingly, the sprocket type may be recognized by determining the ratio between a magnetic perturbation amplitude in a zero- or low-frequency bin Bi , B2... and a magnetic perturbation amplitude in a frequency bin corresponding to the sprocket tooth frequency, i.e. drive motor RPM multiplied with the number of sprocket teeth 30.

[0065] Referring now to Fig. 4, it is a familiar phenomenon that magnetic field lines tend to concentrate at sharp corners. This phenomenon may be used for determining, using the sixth magnetic field sensor 36f, the sharpness of the cutting teeth 17. Blunt cutting teeth 17 will manifest themselves as a lower magnitude of the respective peak in the spectrogram, at a frequency corresponding to the rate at which the cutting teeth pass by the sixth magnetic field sensor 36f. The cutting tooth pass rate may be determined based on the RPM of the drive motor 22 (Fig. 1 ). Blunt cutting teeth 17 may also manifest themselves in the reduction of the amplitude of overtones at integer multiples of the cutting tooth pass rate. The magnetic field perturbation generated by the cutting teeth 17 also locally change the direction of the magnetic field. Accordingly, blunt cutting teeth 17 may also manifest themselves in a changed relationship between the magnetic field perturbations along mutually orthogonal axes of the three-dimensional magnetic field sensor 36f.

[0066] The characteristic frequencies of the spectrogram captured by the sixth magnetic field sensor 36f will also differ between different cutting chain types due to, e.g., differences in the cutting tooth profiles (e.g. chisel or chipper teeth), and differences in the cutting tooth arrangement (e.g. full set of teeth v.s. “skip” arrangements). Accordingly, the frequency-domain data generated based on the signal from the sixth magnetic field sensor 36f may also be used for determining the saw chain type, among a set of predetermined, known saw chain types.

[0067] The sixth sensor 36f may also be used for e.g. detecting any movement of the cutting chain’s 16 path in the axial direction, i.e. the direction of the sprocket rotation axes A1 , A2 (Fig. 2). Such movement manifests itself as a change in amplitude in low and / or zero frequency bins over time, due to the constant presence of the chain in front of the sixth sensor 36f. Thereby, e.g. a meandering path of the cutting chain 16, due to e.g. a mismatch between the lateral width G (Fig. 4) of the guide track 18a (Fig. 4) of the guide bar 18 and the corresponding thickness of drive links 16a of the cutting chain 16, which extends into the guide track 18a. (Fig. 4). This enables, inter alia, detecting a state of wear of the guide track 18a.

[0068] Referring back to Fig. 3, the second magnetic field sensor 36b, which is positioned in the XY plane of the guide bar 18, detects the proximity of the cutting chain 16 to the magnetic field sensor 36b. When revving up a chainsaw 10, the cutting chain tends to be deflected in the vertical, i.e. Y (Fig. 1 ), direction at the gap between the cutting chain drive sprocket 28 and the guide bar 18. For a certain acceleration, a certain vertical deflection in the Y direction indicates a correct tension. On the other hand, an overly tensioned or overly loose cutting chain 16 will be deflected to a lower or higher degree than that which corresponds to the correct tension. A change of distance between the cutting chain 16 and the second magnetic field sensor 36b manifests itself as a change of amplitude in all frequency bins B-i-Bn (Fig. 7). By determining the magnitude of vertical deflection as a function of acceleration (which may be calculated based on RPM information received from the motor controller 40), the cutting chain tension may be determined. In the event that an incorrect cutting chain tension is detected, an alert (e.g. tension too high / tension too low) is communicated to the operator via the wireless link 46 and the user interface of the external device 11 .

[0069] In case the tension of the cutting chain 16 is far too loose, or in case e.g. the pitch of the cutting chain 16 does not match the pitch of the cutting chain drive sprocket 28, the drive links 16a may start climbing out of the gaps between the drive sprocket teeth 30. This results in a changed distance between the cutting chain 16 and the fifth sensor 36e. In case the cutting chain 16 starts climbing on the cutting chain drive sprocket 28, there is an imminent risk that the cutting chain will jump off the cutting chain drive sprocket. Accordingly, in response to a detection of an increased amplitude in all frequency bins B-i- Bn, indicating a reduced distance between the cutting chain 16 and the fifth magnetic field sensor 36e, the data processing equipment 42 transmits a stop signal to the motor controller 40 so as to immediately stop the drive motor 22 (Fig. 1 ) from driving the cutting chain drive sprocket 28. Alternatively or additionally, the data processing equipment 42 (Fig. 6) may also send a stop signal to a chain brake actuator (not illustrated), and / or alert the operator, for example via the external device 11 (Fig. 1 ) or a sound emitter (not illustrated) arranged within the power head 12 (Fig. 1 ). The occurrence of the cutting chain 16 climbing on the cutting chain drive sprocket 28 may also be detected using the second magnetic field sensor 36b, since such climbing can be distinguished from e.g. a somewhat overly slacked cutting chain 16 in that the distance change resulting from chain climbing may occur regardless of the acceleration rate of the chainsaw 10. An imminent chain jump risk may be detected also using e.g. the first magnetic field sensor 36a adjacent to the nose sprocket 34, wherein climbing of the cutting chain 16 on the nose sprocket 34 may be detected as an increasing distance between the first magnetic field sensor 36a and the cutting chain 16. Fig. 11 is a flow chart illustrating a method of determining a structural condition of the cutting chain assembly 15 of the chainsaw 10 (Fig. 1 ). The method comprises the steps 101-103 below.

[0070] In step 101 , time-variant sensor data Si, S2...Sn (Fig. 7) is received from the magnetic detection assembly 36 (Fig. 2);

[0071] In step 102, the time-variant sensor data Si, S2...Sn is converted to frequency domain to obtain a magnitude at each of one or more frequency bins Bi , B2...Bn(Fig. 7) associated with a respective magnetic field perturbation frequency; and

[0072] In step 103, based on the one or more respective magnetic field perturbation frequencies, which may be exemplified by the magnetic field perturbation frequencies illustrated i the first spectrogram 50a of Fig. 8A, and a reference frequency pattern, which may be exemplified by the second spectrogram 50b of Fig. 8B, the structural condition is determined.

[0073] While various structural conditions of the cutting chain assembly 15 (Fig. 1 ) may be detected based on the identification of characteristic frequencies in the magnetic field perturbation spectrum, it will be appreciated that such identification may be performed by a trained classifier, which is trained on various combinations of cutting chains 16 of different states of wear, cutting chain drive sprockets 28 of different states of wear, cutting chain tensions, and RPMs. Accordingly, the processing equipment 42 may comprise such a trained classifier configured to determine, based on the detected magnetic field perturbation, such structural conditions of the cutting chain assembly 15.

[0074] Fig. 12 illustrates a data carrier 98, embodied as a CD-ROM, carrying a trained classifier as described above.

[0075] The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims. For example, the invention has been described with reference to a chainsaw having a cutting chain adapted for cutting wood. The invention is equally applicable to a handheld power cutter of the type having a cutting chain provided with abrasive cutting element for cutting, for example, concrete. The data processing equipment 42 (Fig. 6) has been illustrated as being comprised in the power head 12 (Fig. 1 ). However, the data processing equipment 42 may equally well be comprised in e.g. the device 11 separate from the power cutter (Fig. 1 ), and receive unprocessed sensor data directly from the magnetic detection assembly 36 (Fig. 2).

[0076] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

Claims

Claims1 . A cutting system comprising a handheld power cutter (10), the handheld power cutter (10) comprising a power head (12) comprising a drive motor (22); and a cutting chain assembly (15) comprising a cutting chain drive sprocket (28) configured to be rotated by the drive motor (22) about a drive sprocket axis (A1 ), a guide bar (18) extending from the power head (12), and a cutting chain (16) guided along the guide bar (18), characterized in that the cutting system (8) comprises a magnetic detection assembly (36) comprising at least one magnetic field sensor (36a, 36b, 36c, 36d, 36e, 36f) configured to detect a magnetic field perturbation generated by the cutting chain assembly (15); and data processing equipment (42) configured to receive sensor data from the magnetic detection assembly (36); and determine, based on a detected magnetic field perturbation, at least one structural condition of the cutting chain assembly (15).

2. The cutting system according to claim 1 , wherein said data processing equipment (42) is configured to determine said at least one structural condition of the cutting chain assembly (15) based on a detected magnetic field perturbation frequency pattern (50a, 50b).

3. The cutting system according to any of the preceding claims, wherein said data processing equipment (42) is further configured to receive said sensor data from the magnetic detection assembly (36) as time-variant sensor data (Si-Sn); and convert said time-variant sensor data (Si-Sn) to frequency domain.

4. The cutting system according to claim 3, wherein said data processing equipment (42) is further configured to identify, based on frequency data obtained by said conversion, a magnitude at each of one or more frequency bins (Bi-Bn) associated with a respective magnetic field perturbation frequency.

5. The cutting system according to claim 4, wherein said data processing equipment (42) is further configured to determine a ratio between a magnitudeat a first frequency bin associated with a first magnetic field perturbation frequency, and a magnitude at a second reference frequency bin.

6. The cutting system according to any of the preceding claims, wherein said determination of at least one structural condition of the cutting chain assembly(15) is further based on a determined RPM of the drive motor (22).

7. The cutting system according to any of the preceding claims, wherein said at least one magnetic field sensor (36a, 36b, 36c, 36d, 36e, 36f) is positioned at a distance from the cutting chain assembly (15) of less than 150 mm.

8. The cutting system according to any of the preceding claims, wherein said cutting chain drive sprocket (28) comprises a set of sprocket teeth (30), a radially outermost tip (30a) of which is configured to follow a circular drive sprocket tooth path (P1 ) about the drive sprocket axis (A1 ), wherein the at least one magnetic field sensor (36a, 36b, 36c, 36d, 36e, 36f) comprises a magnetic field sensor (36b, 36d, 36e, 36f) positioned at a distance of less than 50 mm from said drive sprocket tooth path (P1 ).

9. The cutting system according to any of the preceding claims, wherein said guide bar (18) comprises a nose sprocket (34) meshing with the cutting chain(16), the nose sprocket (34) comprising a set of nose sprocket teeth (34a), a radially outermost tip (34b) of which is configured to follow a circular nose sprocket tooth path (P2) about a nose sprocket axis (A2), wherein the at least one magnetic field sensor (36a, 36b, 36c, 36d, 36e, 36f) comprises a magnetic field sensor (36a) positioned at a distance of less than 50 mm from said nose sprocket tooth path (P2).

10. The cutting system according to any of the preceding claims, wherein said at least one magnetic field sensor (36a, 36b, 36c, 36d, 36e, 36f) comprises a magnetoresistive sensor (36a, 36b, 36d, 36e, 36f), such as a tunnel magnetoresistive sensor, or a fluxgate magnetometer (36c).11 .The cutting system according to any of the preceding claims, wherein said at least one magnetic field sensor (36a, 36b, 36c, 36d, 36e, 36f) comprises a three-dimensional sensor.

12. The cutting system according to any of the preceding claims, wherein said at least one magnetic field sensor (36a, 36b, 36c, 36d, 36e, 36f) comprises at least one magnetic field sensor (36a, 36b, 36d, 36e) positioned in a plane (XY) defined by the guide bar (18).

13. The cutting system according to any of the preceding claims, wherein said at least one magnetic field sensor (36a, 36b, 36c, 36d, 36e, 36f) comprises a magnetic field sensor (36c, 36f) positioned outside a plane (XY) defined by the guide bar.

14. The cutting system according to any of the preceding claims, wherein said data processing equipment (42) is configured to store data samples (S-i-Sn) captured by said at least one magnetic field sensor (36a, 36b, 36c, 36d, 36e, 36f) at a sampling rate exceeding 100 Hz.

15. The cutting system according to any of the preceding claims, wherein said data processing equipment (42) is further configured to, based on said determination of at least one structural condition of the cutting chain assembly (15), automatically stop the cutting chain drive sprocket (28).

16. The cutting system according to any of the preceding claims, wherein said data processing equipment (42) is further configured to, based on said determination of at least one structural condition of the cutting chain assembly (15), generate an alert signal to a user of said cutting system (8).

17. The cutting system according to any of the preceding claims, wherein the magnetic detection assembly (36) further comprises at least one magnet (44) configured to generate a baseline magnetic field across at least a portion of said cutting chain assembly (15), and the at least one magnetic field sensor (36a, 36b, 36c, 36d, 36e, 36f) is configured to detect a perturbation, generated by the cutting chain assembly (15), of the baseline magnetic field.

18. The cutting system according to any of the preceding claims, wherein the magnetic detection assembly (36) is a passive magnetic detection assembly (36).

19. The cutting system according to any of the preceding claims, wherein said data processing equipment (42) comprises a trained classifier configured to determine, based on the detected magnetic field perturbation, said at least one structural condition of the cutting chain assembly (15).

20. The cutting system according to any of the preceding claims, wherein said at least one structural condition of the cutting chain assembly (15) comprises at least one of a state of wear of the cutting chain (16), a state of wear of the cutting chain drive sprocket (28), a state of wear of the guide bar (18), a cutting chain type, a drive sprocket type, and a cutting chain tension.

21. The cutting system according to any of the preceding claims, comprising at least one magnetic field sensor (36b) configured to detect a deflection of the cutting chain (16) in a direction (Y) perpendicular to a longitudinal axis (X) of the guide bar (18), along a plane (XY) defined by the guide bar (18), wherein said at least one structural condition of the cutting chain assembly (15) comprises a cutting chain tension.

22. A trained classifier trained to determine, based on a detected magnetic field perturbation from a magnetic detection assembly (36), at least one structural condition of a cutting chain assembly (15) of a handheld power cutter (10).

23. A method of determining a structural condition of cutting chain assembly (15) of a handheld power cutter (10), comprising: receiving time-variant sensor data (S-i-Sn) from a magnetic detection assembly (36); converting said time-variant sensor data to frequency domain to obtain a magnitude at each of one or more frequency bins (Bi-Bn) associated with a respective magnetic field perturbation frequency; and based on the one or more respective magnetic field perturbation frequencies and a reference frequency pattern, recognizing said structural condition.

24. The method according to claim 23, comprising determining a ratio between a magnitude at a first frequency bin associated with a first magnetic field perturbation frequency, and a magnitude at a second reference frequency bin.

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