SE539698C2 - Method for diagnosing power tool condition. - Google Patents

Abstract

Abstract. A method and a device for diagnosing the condition of a powertool and predicting forthcoming power tool malfunctions, whereinthe method comprises the following features: pre-establishingreference characteristics by detecting vibratory movements inthe power tool housing (lO) of a correctly functioning powertool, detecting and recording vibratory movements in the powertool housing (lO) during operation, and determining occurringdiscrepancies between vibratory movements detected in the toolhousing (lO) during operation and said reference characteristicsto indicate the present power tool condition and enable prediction of forthcoming malfunction of the power tool.

Description

Method for diagnosing power tool condition.

The invention relates to a method and a device for detecting anddiagnosing the condition of a power tool. In particular theinvention concerns a method for avoiding future productionproblems by obtaining premature indications on forthcomingmalfunctions of a power tool. Malfunctions that may occur areusually related to mechanical wear and failure of certain partsof the tool, for instance deformed teeth of reduction or angletype gearings, worn down bearings etc. These types ofmalfunctions may occur on different types of tools but wouldhave the most decisive influence on the operation of powerwrenches, especially when used at assembly lines where anunforeseen need for replacement of a malfunctioning tool would cause costly production disturbances.

In prior art there are described a number of different methodsfor this purpose all having been proved less reliable and/or toocomplicated to be practically useful. One such method comprisesstudying of the characteristics of the delivered output torquelooking for abnormal fluctuations in view of time or angle ofrotation. At power wrenches this is carried out by analyzingsignals from a torque sensing device incorporated in the wrench,usually in combination with an angle encoder on the output shaft.

In case of electrically powered power tools there are previouslydescribed methods for discovering and predicting malfunctions byanalyzing the characteristics of the supplied electric power perse or in view of the indicated output torque of the tool.Discrepancies found in such analyzes would indicate possibleforthcoming malfunctions. A drawback of this known method is its limitation to electric tools only.

Still another method for predicting future malfunctions of apower tool is based on counting the actual number of workingcycles performed by the tool and establishing whether the actual number of operation cycles would create a statistic risk of failure or breakdown in view of a normal maximum operation cycles to be expected by the actual type of tool.

The methods described in prior art are less reliable,complicated or do not give a complete picture of what the reasonmay be for the indicated irregularities in the power tool function.

It is an object of the invention is to solve the problemsinherent in prior art method by providing a power tool functionanalyzing method which is universally applicable on differenttypes of power tools and which is able to give a complete picture of what causes occurring irregularity indications.

So, an object of the invention is to provide a reliable method and a device for predicting forthcoming malfunctions of a powertool which is universally applicable on power tools of differentkinds and which does not require any redesign of the power tool parts.

It is a further object of the invention to provide a method anda power tool by which forthcoming malfunction problems may bepredicted by studying and analyzing different types of occurringvibrations to which the power tool housing may be subjected during tool operations.

Further objects and advantages of the invention will appear from the following specification and claims.

A preferred embodiment of the invention is described below in detail with reference to the accompanying drawing.

In the drawing Fig. I shows, partly in section, a side view of a power toolaccording to the invention.

Fig. 2 shows on a larger scale a handle section of the powertool in Fig. I illustrating a vibration detecting device.

Fig. 3 shows schematically three power tools communicating bothwith separate operation control units each connected to a common signal analyzing and fault detecting unit.

Fig. 4 shows a torque/speed-to-angle diagram of a typical two-step screw joint tightening process.

Fig. 5 shows a torque/acceleration-to-angle diagram illustratingvibratory movements indicated in the tool housing of normallyoperating power wrench during a two-step tightening process.Fig. 6 shows a diagram similar to Fig. 5 but illustratingincreased vibration amplitudes indicating some mechanical wear or damage.

The power tool illustrated in Fig. l is an electric angle typepower wrench which comprises a housing lO with a handle ll atits rear end and an angle drive head l2 at its forward end. Onthe handle ll there is supported a power control trigger l3 anda connection socket l4 for a combined power and signalcommunicating cable l5. In the angle drive head l2 there issupported an angle gearing and a square ended output shaft l7for connection to a nut socket. Within the housing lO there issupported a non-illustrated motor and a reduction gearing whichare connected to the output shaft l4 via the angle gearing. Themotor, and the reduction and angle gearings are of aconventional types and, therefore, a detailed description thereof are left out of this specification.

In the handle ll, which is connected to and forms a rigid unittogether with the housing lO, there is mounted a combined gyroand accelerometer unit 24 which is arranged to detect vibratorymovements of the housing lO in three different planes. This gyroand accelerometer unit 24 comprises a programmable chip and anumber of electric components affixed to a printed circuit board25 mounted on a bracket 26 in the handle ll. A flat type ofwiring 27 is connected to the circuit board 25 and communicatessignals from the unit 24 to a signal receiving and analyzingunit which could be located inside the power tool housing itself or in a separate unit 22.

The gyro and accelerometer unit 24, which in itself is of a commercially available type, may detect vibratory movements in three different planes forming right angles relative to eachother. Since different types of faults related to gearings orbearings of the power tool will cause tool housing vibrations indifferent directions it will be possible to detect different kinds of forthcoming malfunctions of the tool.

The reference data stored for analyzing purposes shouldcorrespond to vibratory movements in different directionsreflecting different types of faults that may occur in the power wrench and detected by the gyro and accelerometer unit 24.

So, signals responding to detected vibrations induced in thehousing lO during operation of the power wrench are received bya signal receiving and analyzing unit and compared to referencedata relating to vibratory housing movements of a normallyfunctioning power wench. So, by comparing these reference datawith vibratory movements detected in the power wrench housingduring operation it is possible to discover occurringdiscrepancies between the reference data and the signals emittedduring operation and thereby obtain an indication on possible forthcoming malfunctions of the tool.

A signal receiving and analyzing unit may be located atdifferent places, for instance in an operation control unit 22a-c separated from the power tool wherein emitted vibrationrelated signals are communicated via the combined power andsignal cable to the operation control unit. The analyzingprocess may be performed in the operation control unit orcommunicated further to a common central unit 30. In Fig. 3there are illustrated three identical power wrenches a, b and ceach connected to a separate operation control unit 22 a-c viacables l5 a-c, wherein the units 22 a-c are connected to acommon central signal analyzing and fault detecting unit 30.Identification as well as reference data valid for each one ofthe power wrenches are stored in this central unit 30 and alert signals will be emitted as vibration related signals received from either one of the power wrenches differ from the stored reference data.

A typical two-step screw joint tightening process is illustratedby a torque/speed to rotation angle diagram in Fig. 4, whereinthe torque output in relation to rotation angle R from the powerwrench is illustrated by curve T and the rotation speed by curveV. The two-step tightening process comprises an initial highspeed running down phase A wherein the resistance from the screwjoint is low and a low speed pre-tensioning phase B during an increased torque and screw joint pre-tensioning level.

In Fig. 5 there is illustrated a torque/acceleration to anglediagram illustrating vibratory movements indicated in the toolhousing of normally operating power wrench during a two-steptightening process as illustrated in Fig. 4. Also in thisdiagram the torque output from the power wrench is illustratedby curve T, whereas the detected acceleration Y is illustratedby curve Yl. The curve Yl is responsive to the signal emitted bythe gyro and accelerometer unit 24 during operation of anormally functioning power wrench, i.e. a power wrench where nonoticeable mechanical wear or damage has been detected. It is tobe noted, though, that the ripple frequency of the emittedsignal is constant during the high speed running down phase Abut is lower during the slower pre-tensioning phase B. The frequency corresponds to the rotation speed of the power wrench.

The diagram shown in Fig. 6 is similar to that of Fig. 5 but theamplitude of the signal ripple of the acceleration curve Y2 isbigger in comparison with the curve Yl of Fig. 5 which is areference curve representative of a normally functioning powerwrench. This change in amplitude or character of the signalripple indicates that some mechanical wear or other changes tothe power transmission of the power wrench has occurred and thata forthcoming malfunction of the power wrench is to be expected.This indication makes it possible to predict forthcoming tool problems and to plan for a premature replacement of the power wrench thereby avoiding a later production disturbance due to tool failure.

It is to be understood, however, that the invention is notlimited to the above described example but may be freely variedwithin the scope of the claims. For instance, the invention mayvery well be applied on battery powered tools wherecommunication with remote operation control and supervising units are performed via wireless transmission.

Claims (7)

Claims.

1. l. A method for diagnosing the condition of a power toolcomprises the following features, 0 pre-establishing reference characteristics of vibratorymovements in the power tool housing of a correctlyfunctioning power tool, 0 detecting and recording vibratory movements in the powertool housing during operation, and 0 determining occurring discrepancies between vibratorymovements detected in the tool housing during operationand said reference characteristics to indicate the presentpower tool condition and enable prediction of forthcoming malfunction of the power tool.

2. Method according to claim l, wherein said pre-established reference characteristics are related to differentpossible malfunction sources of the tool, and comparingoccurring vibratory movements indicated in the tool housingduring tool operation with said pre-established referencecharacteristics to establish what specific malfunction to be expected.

3. Method according to claim l or 2, wherein vibratorymovements of the power tool housing are detected in at least two different planes.

4. Method according to claim 3, wherein said at least twodifferent planes comprise three planes located at right angles relative each other.

5. Power tool intended for performing the methodaccording to claims l -4, comprising a housing (lO), a motor, anoutput shaft (l7) and a gearing connecting the motor the output shaft (l7), said housing (lO) carrying a vibration detecting device (24) arranged to emit signals in relation to vibratory movements of the housing (10) in at least two different planes.

6. Power tool according to claim 5, wherein saidvibration detecting device (24) is connected to a signalreceiving and analyzing unit (22 a-c, 30) having storedreference data on vibratory movements of the housing (l0) at acorrectly functioning power tool, wherein said signal receivingand analyzing unit (22 a-c, 30) comprises means for establishingoccurring discrepancies between said stored reference data and vibratory related signals received during tool operation.

7. Power tool according to claim 5 or 6, wherein saidvibration detecting device (24) comprises a combined gyro and accelerometer unit.