WO2023274624A1

WO2023274624A1 - Method of detecting clutch release in a tightening tool

Info

Publication number: WO2023274624A1
Application number: PCT/EP2022/063697
Authority: WO
Inventors: Guillermo BOSSI; Daniel Eriksson
Original assignee: Atlas Copco Industrial Technique Ab
Priority date: 2021-06-28
Filing date: 2022-05-20
Publication date: 2023-01-05
Also published as: CN117545594A; SE545684C2; EP4363166A1; SE2130177A1

Abstract

A method of detecting clutch release in a tightening tool (1) comprising an electric motor (11) and a clutch (9), the method comprising: a) determining, for each of a plurality of first values of a first motor or battery parameter obtained while the torque of the electric motor(11) is increasing, whether the first value fulfils a first clutch release indicator threshold criterion, and b) decreasing the speed of the electric motor (11) if one of the first values fails to fulfil the first clutch release indicator threshold criterion and a later first value fulfils the first clutch release indicator threshold criterion. A tightening tool (1) for performing the method is also provided.

Description

METHOD OF DETECTING CLUTCH RELEASE IN A TIGHTENING TOOL

TECHNICAL FIELD

The present disclosure generally relates to electrically powered tightening tools.

BACKGROUND

Industrial tightening tools such as nutrunners are widely used in the manufacturing industry, for example in vehicle manufacturing and the aerospace industry.

It is usually required that the operator receives feedback about the status of each tightening operation. Thus, for each nut, bolt, or screw that has been tightened, the operator needs to be ensured that the tightening has been made correctly, i.e. with the prescribed torque. The applied torque may also be documented in a database for each nut, bolt, or screw for all the work pieces that are manufactured.

Tightening tools may comprise a clutch that is released when the bolt, screw, or nut has been tightened with the prescribed torque. This provides an indication to the operator that the tightening has been performed according to specifications. To be able to provide correct feedback to the operator and/or for database documentation, the clutch release has to be accurately detected.

SUMMARY

In view of the above, an object of the present disclosure is to provide a method which solves, or at least mitigates, problems of the prior art. There is hence according to a first aspect of the present disclosure provided a method of detecting clutch release in a tightening tool comprising an electric motor and a clutch, the method comprising: a) determining for each of a plurality of first values of a first motor or battery parameter obtained while the torque of the electric motor is increasing whether the first value fulfils a first clutch release indicator threshold criterion, and b) decreasing the speed of the electric motor if one of the first values fails to fulfil the first clutch release indicator threshold criterion and a later first value fulfils the first clutch release indicator threshold criterion .

The clutch release may thereby be determined in an accurate manner. The clutch release may in particular be determined without any additional sensor than that/those required for monitoring and controlling the operation of the electric motor. Thus, clutch release detection may be made without employing additional hardware than what is already provided in electrically powered tightening tools on the market.

Further, due to the braking of the electric motor in step b), the operator receives feedback that the clutch has been released and thus that the tightening has been performed according to specifications.

In step b) the decreasing of the speed may involve stopping the electric motor.

According to one embodiment the first motor or battery parameter is a motor speed, a motor torque, a motor current, a battery current or a battery voltage. Each one of the motor speed, the motor torque, the motor current, the battery current and the battery voltage provides an indication of the clutch being released.

According to one embodiment step a) comprises determining for each of a plurality of a second values of a second motor or battery parameter obtained while the torque of the electric motor is increasing whether the second value fulfils a second clutch release indicator threshold criterion, wherein step b) comprises decreasing the speed of the electric motor if also one of the second values fails to fulfil the second clutch release indicator threshold criterion and a later second value fulfils the second clutch release indicator threshold criterion.

In some cases, one motor or battery parameter may provide a false indication of clutch release. For example, in case the first motor or battery parameter is motor torque, the motor torque will decrease also if the tightening tool loses mechanical contact with the screw/bolt/nut joint. In case two threshold criteria have to be fulfilled, i.e. the first and the second clutch release indicator threshold criterion, after failing to be fulfilled the detection of clutch release can be made more reliably.

According to one embodiment the second motor or battery parameter differs from the first motor or battery parameter and is a motor speed, a motor torque, a motor current, a battery current or a battery voltage.

According to one embodiment the first motor parameter is the motor torque or motor current, and the first clutch release indicator threshold criterion is that the first value is smaller than a threshold value. The motor torque and motor current decrease drastically when the clutch is released and the load is removed, thus providing an indication of the clutch release.

According to one embodiment the second motor parameter is the motor speed, and the second clutch release indicator threshold criterion is that the second value is larger than a threshold value. The motor speed increases drastically when the clutch is released thus providing an indication of the clutch release.

According to one embodiment the first motor parameter is the motor speed, and the first clutch release indicator threshold criterion is that the first value is larger than a threshold value.

According to one embodiment the second motor parameter is the motor torque or motor current, and the second clutch release indicator threshold criterion is that the second value is smaller than a threshold value.

The first battery parameter may be a battery voltage or a battery current.

When the clutch is released and the motor speed increases, the controller of the tightening tool is configured to try to decrease the motor speed causing current to flow from the electric motor to the battery. This results in that the battery voltage is temporarily increased and the battery current decreases. Thus, in case the first battery parameter is the battery voltage, the first clutch release indicator threshold criterion may be that the first value is larger than a threshold value. In case the first battery parameter is the battery current, the first clutch release indicator threshold criterion may be that the first value is smaller than a threshold value.

The second battery parameter may be a battery voltage or a battery current. In case the second battery parameter is the battery voltage, the second clutch release indicator threshold criterion may be that the second value is larger than a threshold value. In case the second battery parameter is the battery current, the second clutch release indicator threshold criterion may be that the second value is smaller than a threshold value.

One embodiment comprises determining whether a third value of the first motor or battery parameter, obtained after the first value which fulfils the first clutch release indicator threshold criterion was obtained, fulfils a third clutch release indicator threshold criterion, wherein step b) involves decreasing the speed of the electric motor only if also the third clutch release indicator threshold criterion is fulfilled.

Thus, after a first value that fulfils the first clutch release indicator threshold criterion has been obtained or measured, a value, here termed "third value", of the same, i.e. the first motor or battery parameter, is obtained or measured, and it is determined whether the third value fulfils the third clutch release indicator threshold criterion.

The third value may for example be measured a predetermined amount of time after the first value was obtained or measured. According to one embodiment the first motor or battery parameter is the motor torque or motor current, and the third clutch release indicator threshold criterion is that the third value is larger than a threshold value.

Each of the motor torque and the motor current has a characteristic behaviour in the process of the clutch being released. The motor torque and current first fall but then rise, before falling again. Thus, by detecting this behaviour by means of determining whether the first value fulfils the first clutch release indicator threshold criterion followed by the third value fulfilling the third clutch release indicator threshold criterion, it may be possible to reliably determine the clutch release by monitoring a single motor parameter. False indications due to for example the tightening tool losing mechanical contact with the screw/bolt/nut joint may thus be discarded.

According to one embodiment the first motor or battery parameter is the motor speed, and the third clutch release indicator threshold criterion is that the third value is smaller than a threshold value.

There is according to a second aspect of the present disclosure provided a tightening tool comprising: an output shaft, an electric motor, a clutch configured to connect the electric motor to the output shaft, and a controller configured to control the electric motor, the controller comprising: storage medium comprising computer code, and processing circuitry configured to execute the computer code, causing the tightening tool to perform the method of the first aspect. Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, etc.", unless explicitly stated otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 schematically shows a perspective view of an example of a tightening tool;

Fig 2 schematically shows an example of a clutch of the tightening tool in Fig. 1;

Fig. 3 schematically shows a block diagram of an example of the tightening tool in Fig. 1;

Fig. 4 is a flowchart of a method of detecting clutch release in a tightening tool comprising an electric motor and a clutch;

Fig. 5 shows a graph of the torque and the motor speed when the clutch is released; and

Fig. 6 is a graph in addition to the torque and motor speed shows the battery current and battery voltage when the clutch is released. DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description.

Fig. 1 shows an example of a tightening tool 1. The tightening tool 1 is an electrically powered tightening tool.

The tightening tool 1 may be cordless or electrically powered via a cord.

The tightening tool 1 may for example be a nutrunner or a screwdriver. The tightening tool 1 has a tool head 3 and a main body

5. The tool head 3 is attached to the main body 5. The tool head 3 is in the example straight but could alternatively be angled.

The tool head 3 has an output shaft 3a. The output shaft 3a is configured to be rotatably driven and engage with a fastener such as a nut, a bolt, or a screw.

The tightening tool 1 has a housing 7. The tightening tool 1 comprises an electric motor configured to drive the output shaft 3a. The electric motor is arranged in the housing 7.

Fig. 2 shows an example of some internal components of the tightening tool 1. The tightening tool 1 comprises a clutch 9 configured to connect the electric motor 11 to the output shaft 3a.

The electric motor 11 has a stator (not shown), and a rotor (not shown) configured to rotate relative to the stator. The rotor is configured to be connected to the output shaft 3a via the clutch 9.

The tightening tool 1 comprises gears 12 connecting the rotor to the clutch 9.

The exemplified clutch 9 comprises a rotatable shaft 9a, which is the output shaft 3a or which is rotatably fixed relative to the output shaft 3a, a coil spring 9b provided around the shaft 9a, a first disc 9c rotationally fixed relative to the shaft 9a, and a second disc 9d which is rotationally fixed relative to the rotor.

The spring 9b pushes the first disc 9c against the second disc 9d which thereby engage such that the rotation of the rotor and the second disc 9d is transferred to the first disc 9c and the shaft 9a. The first disc 9c and the second disc 9d have balls 9e arranged between them, which prevent relative rotation between the two discs 9c, 9d as long as the torque is smaller than a threshold value. The spring 9b is calibrated to a stiffness such that the clutch 9 is released at a specified torque, i.e. the threshold value. As a nut, bolt or screw is tightened by the rotation of the output shaft 3a the torque eventually increases to the specified level required for the clutch 9 to release. The clutch 9 is released when the first disc 9c and the second disc 9d disengage, causing the spring 9b to compress and the first disc 9c and the second disc 9d to rotate relative to each other.

Fig. 3 schematically shows a block diagram of an example of the tightening tool 1. The exemplified tightening tool 1 comprises a controller 13 configured to control the electric motor 11. The controller 13 comprises a storage medium 13a comprising computer code, and processing circuitry 13b configured to execute the computer code, causing the tightening tool 1 to perform the method (s) as disclosed herein.

The storage medium 13a may for example be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read only memory (EEPROM) and more particularly as a non volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory.

The processing circuitry 13b may for example use any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital processor (DSP), application specific integrated circuit (ASIC), field programmable gate arrays (FPGA) etc.

The tightening tool 1 may comprise power electronic circuitry 17 configured to control the electric motor 11. The controller 13 may be configured to control the power electronic circuitry 17 to thereby control the speed and/or the torque of the electric motor 11.

The tightening tool 1 may comprise a battery 19 connected to the power electronic circuitry 17 to power the electric motor 11. Control of the power electronic circuitry 17 by the controller 13 may cause modulation of the battery current fed to the power electronic circuitry 17 from the battery 19 to thereby control the speed of the electric motor 11.

The electric motor 11 may comprise an angle sensor 15 configured to determine the angle of the rotor. The controller 13 may be configured to determine the speed of the electric motor 11 based on the angle. Alternatively, the controller 13 may be configured to determine the angle by means of a sensorless method.

The tightening tool 1 may comprise a motor current sensor (not shown) configured to determine the motor current.

The controller 13 may be configured to determine the motor torque based on the motor current, which is proportional to the motor torque.

The tightening tool 1 may comprise a battery voltage sensor (not shown) configured to measure the battery voltage. The tightening tool 1 may comprise a battery current sensor (not shown) configured to measure the battery current.

A method of detecting clutch release in the tightening tool 1 by means of the controller 13 will now be described with reference to Figs 4-6. In a step a) it is determined for each of a plurality of first values of a first motor or battery parameter, i.e. a first motor parameter or a first battery parameter, whether, the first value fulfils a first clutch release indicator threshold criterion.

The first values may be measurements obtained from a sensor or each may be determined by the controller 13 based on a measurement from a sensor, such as in the case that the first motor parameter is the motor torque.

The first motor parameter may be one of the motor speed, the motor torque, and the motor current.

The first battery parameter may be one of the battery current and the battery voltage.

According to one example, step a) may involve determining for each of a plurality of second values of a second motor or battery parameter, i.e. a second motor parameter or a second battery parameter, whether the second value has a second value that fulfils a second clutch release indicator threshold criterion.

The second motor parameter differs from the first motor parameter and may be one of the motor speed, the motor torque, and the motor current.

The second battery parameter differs from the first battery parameter and may be one of the battery current and the battery voltage.

The second values may be measurements obtained from a sensor or each may be determined by the controller 13 based on a measurement from a sensor. In a step b) the speed of the electric motor is decreased if one first value fails to fulfil the first clutch release indicator threshold criterion and a later obtained first value fulfils the first clutch release indicator threshold criterion. The decreasing may involve stopping the electric motor 11.

The plurality of first values and/or second values may be obtained as long as the tightening tool 1 is being operated and the torque is increasing.

If step a) involves determining whether second value fulfils a second clutch release indicator threshold criterion, step b) involves decreasing the speed of the electric motor only if also one second value fails to fulfil the second clutch release indicator threshold criterion followed by a second value which fulfils the second clutch release indicator threshold criterion.

One example comprises determining whether a third value of the first motor or battery parameter, obtained or measured after a first value which fulfils the first clutch release indicator threshold criterion, fulfils a third clutch release indicator threshold criterion. The third value of the first motor or battery parameter may be obtained or measured a predetermined amount of time after the first value which fulfils the first clutch release indicator threshold criterion was obtained or measured. Alternatively, or additionally, the third value may be obtained or measured repeatedly after it has been determined that the first value fulfils the first clutch release indicator threshold criterion. Each third value measurement may be compared with the third clutch release indicator threshold criterion. In case the third clutch release indicator threshold criterion is fulfilled, and the first clutch release indicator threshold criterion has already been fulfilled, it is determined that the clutch has been released. Step b) involves decreasing the speed of the electric motor also the third clutch release indicator threshold criterion is fulfilled. The first motor or battery parameter may be a first motor parameter which is the motor torque or motor current. The third clutch release indicator threshold criterion is then that the third value is larger than a threshold value.

Alternatively, the first motor parameter is the motor speed, and the third clutch release indicator threshold criterion is that the third value is smaller than a threshold value. Fig. 5 illustrates examples of the first/second motor parameter in the form of motor torque in curve 21 and motor speed in curve 23. The motor torque scale is shown to the left and the motor speed scale is shown to the right in the graph. The clutch 9 is released at around 0.2 s, indicated by the vertical dashed line 25. As can be seen the motor torque 21 decreases to 0 Nm and the motor speed increases with more than 1000 RPM.

In case the first/second motor parameter is the motor torque, it is determined whether the first/second value, which is the motor torque at a given instance in time, fulfils the first/second clutch release indicator threshold criterion which is that the first/second magnitude is smaller than a threshold value. The threshold value may for example be that the first/second value is at least 50% smaller than the value of the motor torque prior to the clutch release, although other possible threshold values are also envisaged herein.

If the first/second motor parameter is the motor speed, it is determined whether the first/second value, which is the value of the motor speed at a given instance in time, fulfils the first/second clutch release indicator threshold criterion which is that the first/second value is larger than a threshold value. The threshold value may for example be that the first/second value is at least 20% larger than the motor speed prior to the clutch release, although other possible threshold values are also envisaged herein.

The motor torque behaves characteristically when the clutch releases. The motor torque initially decreases after the clutch has released, followed by a temporary increase as shown by arrow 26. It is this characteristic behaviour that can be captured by means of the third value and the third clutch release indicator threshold criterion.

In Fig. 6 the graph depicts examples of the first/second battery parameter in the form of battery current in curve 27 and battery voltage in curve 29. The battery current scale is shown to the left and the battery voltage scale is shown to the right in the graph.

The clutch 9 is released at around 0.22 s, indicated by the vertical dashed line 31. As can be seen the battery current decreases to 0 A and the battery voltage increases substantially.

The inventive concept has mainly been described above with reference to a few examples. 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 inventive concept, as defined by the appended claims.

Claims

1. A method of detecting clutch release in a tightening tool (1) comprising an electric motor (11) and a clutch (9), the method comprising: a) determining, for each of a plurality of first values of a first motor or battery parameter obtained while the torque of the electric motor (11) is increasing, whether the first value fulfils a first clutch release indicator threshold criterion, and b) decreasing the speed of the electric motor (11) if one of the first values fails to fulfil the first clutch release indicator threshold criterion and a later first value fulfils the first clutch release indicator threshold criterion.

2. The method as claimed in claim 1, wherein the first motor or battery parameter is a motor speed, a motor torque, a motor current, a battery current or a battery voltage.

3. The method as claimed in claim 1 or 2, wherein step a) comprises determining, for each of a plurality of second values of a second motor or battery parameter obtained while the torque of the electric motor (11) is increasing, whether the second value fulfils a second clutch release indicator threshold criterion, wherein step b) comprises decreasing the speed of the electric motor (11) if also one of the second values fails to fulfil the second clutch release indicator threshold criterion and a later second value fulfils the second clutch release indicator threshold criterion. i8

4. The method as claimed in claim 3, wherein the second motor or battery parameter differs from the first motor or battery parameter and is a motor speed, a motor torque, a motor current, a battery current or a battery voltage.

5. The method as claimed in any of the preceding claims, wherein the first motor parameter is the motor torque or motor current, and the first clutch release indicator threshold criterion is that the first value is smaller than a threshold value.

6. The method as claimed in claim 2 or any of claims 3-5 dependent of claim 2, wherein the second motor parameter is the motor speed, and the second clutch release indicator threshold criterion is that the second value is larger than a threshold value.

7. The method as claimed in any of claims 1-4, wherein the first motor parameter is the motor speed, and the first clutch release indicator threshold criterion is that the first value is larger than a threshold value.

8. The method as claimed in claim 7 dependent of claim 2, wherein the second motor parameter is the motor torque or motor current, and the second clutch release indicator threshold criterion is that the second value is smaller than a threshold value.

9. The method as claimed in any of the preceding claims, comprising determining whether a third value of the first motor or battery parameter, obtained after the first value which fulfils the first clutch release indicator threshold criterion was obtained, fulfils a third clutch release indicator threshold criterion, wherein step b) involves decreasing the speed of the electric motor only if also the third clutch release indicator threshold criterion is fulfilled.

10. The method as claimed in claim 9, wherein the first motor or battery parameter is the motor torque or motor current, and the third clutch release indicator threshold criterion is that the third value is larger than a threshold value.

11. The method as claimed in claim 9, wherein the first motor or battery parameter is the motor speed, and the third clutch release indicator threshold criterion is that the third value is smaller than a threshold value.

12. A tightening tool (1) comprising: an output shaft (3a), an electric motor (11), a clutch (9) configured to connect the electric motor (11) to the output shaft (3a), and a controller (13) configured to control the electric motor (11), the controller (13) comprising: storage medium (13a) comprising computer code, and processing circuitry (13b) configured to execute the computer code, causing the tightening tool (1) to perform the method of any of claims 1-11.