Pulse tool for tightening joints

Abstract

A pulse tool (1) for tightening joints is provided. The pulse tool comprises a motor (3); an output shaft (2); a pulse unit (4) arranged to be driven by the motor (3) and to deliver torque in pulses to the output shaft (2); a motor angle 5 sensor (7) arranged to output data indicative of a rotation angle output from the motor (3); an output shaft angle sensor (8) arranged to output data indicative of a rotation angle of the output shaft (2); and a control device (10) configured to: determine whether a rotation angle of the output shaft (2) as calculated based on the data from the motor angle sensor (7) and a rotation angle of the output 10 shaft (2) as indicated by the data from the output shaft angle sensor (8) deviates from each other.

Description

[0001]PULSE TOOL FOR TIGHTENING JOINTSField of the inventionThe present invention generally relates to the field of pulse tools for tighteningjoints. In particular, the present invention relates to such tools comprising anangle sensor for measuring an angle of a tightening operation.Background of the invention In industrial assembly, the requirements on ergonomics for operators as well as precision in installed torque in a joint are of high importance. Therefore, so called pulse tools are often used. Pulse tools deliver the tightening torque in pulses, wherein the output torque is zero between each torque pulse. This may be achieved by means of a pulse unit that intermittently couples the motor to the output shaft. Such pulse tools are known for achieving high precision in installed torque as well as low reaction forces for the operators due to the pulsing technique.In tightening technique on an industrial level, it is generally desirable to recordcertain parameters of a tightening for the purpose of traceability and future audit. Such parameters may typically include the torque and the angle of the tightening. These parameters may also be used for controlling the tightening. For example, the tightening may be automatically ended when a target torque or target angle is achieved. In order to record such parameters, adequate sensors are comprised in the tool.EP 1747085 B1 shows a pulse tool comprising an angle sensor arranged forsensing the rotation of an inertia drive member of the pulse unit. The inertiadrive member is rigidly coupled to the rotor of the motor. By detecting themovement of the rotating parts by means of the angle sensor, the rotation speed as well as the retardation magnitude of the rotating parts may be calculated, andby using the calculated retardation magnitude and the total inertia moment ofthe inertia drive member and co-rotating parts of the tool, the torque transferredto the fastener can be determined. Further, the control unit of this tool is alsocapable of determining the angular displacement of the output shaft and thethreaded fastener by using the signals generated by the angle sensor. Since therotational movement of the inertia drive member during each impulsegeneration comprises one full revolution, i.e.360°, plus the resultantdisplacement of the output shaft, the total output shaft angular displacement canbe calculated accordingly. Hence, a single sensor can be used to estimate bothtorque and angle of the tightening. Due to the high requirements on accuracy in industrial tightening operations, further improvements in the field would be desirable. Summary of the inventionIt would be desirable to enable a pulse tool able to achieve even more reliableand accurate tightening operations.To better address one or more of these concerns, a pulse tool having the featuresdefined in the independent claim is provided. Preferable embodiments are defined in the dependent claims.Hence, according to an aspect, a pulse tool for tightening joints is provided. Thepulse tool comprises a motor, an output shaft, a pulse unit arranged to be driven by the motor and to deliver torque in pulses to the output shaft, a motor angle sensor arranged to output data indicative of a rotation angle output from the motor, an output shaft angle sensor arranged to output data indicative of a rotation angle of the output shaft, and a control device. The control device is configured to determine whether a rotation angle of the output shaft as calculated based on the data from the motor angle sensor and a rotation angle of the output shaft as indicated by the data from the output shaft angle sensor deviates from each other. With the present aspect, the motor angle sensor is used forcalculating / estimating the rotation angle (which also may be referred to as theangular displacement) of the output shaft while the output shaft angle sensor isused for measuring the rotation angle (or any parameter indicative thereof) ofthe output shaft (or any component rigidly connected thereto) directly. It is thenpossible to determine if these two rotation angles (i.e. the calculated and the directly measured) deviates from each other. Such deviation may indicate e.g. that one of the sensors is not working properly, whereby the tightening operation, or the recorded results therefrom, may not be accurate / reliable. By being able to detect that, proper actions may be taken at an early stage toprevent further potentially unreliable / inaccurate tightening operations to beperformed. Hence, in general, more reliable and accurate tightening operationscan be provided.It will be appreciated that the motor angle sensor may be arranged to sense therotation of any part of the driveline rigidly coupled to a rotor of the motor. For example, it may be arranged at the rotor itself or at an inertia drive member of the pulse unit being rigidly coupled to the rotor of the motor.In similarity, the output shaft angle sensor may be arranged to sense the rotationof any part of the driveline rigidly coupled to the output shaft. For example, itmay be arranged at the output shaft itself or any component co-rotating with the output shaft.The pulse unit may e.g. be a hydraulic pulse unit comprising a hydrauliccoupling.According to an embodiment, the control device may further be configured totake measure in response to determining that the rotation angle of the output shaft as calculated based on the data from the motor angle sensor and the rotation angle of the output shaft as indicated by the data from the output shaftangle sensor deviates from each other more than to a predetermined extent.For example, measures may be taken when one of the angles deviate more thanone or a few degrees from the other. By taking measure (action), further potentially unreliable / inaccurate tightening operations may be prevented. According to an embodiment, taking measure may comprise at least one of: issue an alert signal, interrupt the ongoing tightening operation and disable the pulsetool (to perform a tightening operation).Hence, an operator may become aware of a potential faulty sensor and / or maybe prevented from continuing the tightening operation and / or to start a newtightening operation. According to an embodiment, the rotation angles (i.e., the calculated angulardisplacement and the directly sensed angular displacement) may be countedfrom a predetermined torque level.Hence, passing the predetermined torque level may be the starting point for theangular measurements. This may also be the starting point for evaluating if thereis a deviation between the calculated angle and the directly sensed angle. Thispredetermined torque level may e.g. be a predetermined percentage (larger thanzero) of the target torque, such as 50% of the target torque. The correlation ofthe angle as indicated by the motor angle sensor to the angle as indicated by theoutput shaft angle sensor may be unpredictable, in particular during therundown phase, since the motor and the output shaft will continuously co-rotateonly as long as the torque is very low (close to zero), but as soon as just some torque is applied (e.g. due to some friction peak during rundown), the pulse unit will operate, whereby the output shaft will no longer co-rotate with the motor. Hence, to have a predictable correlation between the angle as indicated by themotor angle sensor to the angle as indicated by the output shaft angle sensor it ispreferable to start the measurement / comparison when a predetermined torque is exceeded.According to an embodiment, the control device may be configured to determinea total angle of a performed tightening based on the data from the output shaft angle sensor (e.g. as counted from a predetermined torque level). This total angle of the tightening may e.g. be sent to and saved by an assemblymanagement system for traceability (e.g. for future audit purpose).Hence, the angle measurements from the output shaft angle sensor may be the one that are saved together with other tightening parameters for traceability, whereas the angle measurements from the motor angle sensors are used as a reliability check of the angle sensors. According to an embodiment, the control device may be configured to estimatethe torque applied to the fastener based on the data from the motor anglesensor. This may e.g. be made based on an angular retardation as indicated bythe data from the motor angle sensor and a predefined tool constant (related tothe mass of the rotating parts). Thus, no further torque transducer is required,whereby the cost and complexity of the tool can be reduced.According to an embodiment, the pulse tool may comprise an orientation sensor(such as a gyro) arranged to sense an orientation of the pulse tool. The controldevice may be further configured to determine an angle of the tightening basedon the data from the output shaft angle sensor and data from the orientationsensor so as to compensate for any change in orientation angle of the tool madeduring the tightening (by the operator). Hence, in case the operator turns thetool (around the rotation axis of the fastener) during the tightening, the determined (total) angle of the tightening may not be affected, which provides a more reliable end result. It is noted that embodiments of the invention relate to all possible combinations of features recited in the claims. Brief description of the drawingsThis and other aspects will now be described in more detail in the followingillustrative and non-limiting detailed description of embodiments, withreference to the appended drawings.Figure 1 shows a pulse tool according to an embodiment.Figure 2 is a cross section of the upper part of the pulse tool of Figure 1. All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the embodiments, wherein otherparts may be omitted. Like reference numerals refer to like elements throughoutthe description. Detailed description of embodiments A pulse tool 1 according to an embodiment will be described with reference toFigure 1 and 2. The pulse tool 1 is a tightening tool for tightening threadedfasteners in an industrial assembly environment.The pulse tool 1 comprises a motor 3, such as an electric or pneumatic motor.The motor 3 may comprise a stator and a rotor 6. The pulse tool 1 further comprises an output shaft 2, to which a socket (not shown) can be attached. The output shaft 2 may e.g. comprise a square for standardized coupling to sockets. The output shaft 2 is arranged to apply torque to a fastener (mated in the socket). The pulse tool 1 further comprises a pulse unit 4 arranged do be driven by themotor 3 and to drive the output shaft 2. In other words, the pulse unit isarranged between the motor 3 and the output shaft 2 in the driveline of the tool1. The pulse unit 4 may comprise a hydraulic coupling for transforming a continuous torque from the motor 3 into torque pulses on the output shaft 2. The pulse unit 4 may comprise an inertia drive member 5 rigidly coupled (atleast indirectly) to the rotor 6 of motor 3. The pulse unit 4 may further be rigidlycoupled (at least indirectly) to the output shaft 2. For example, the output shaft 2may extend into a hydraulic chamber 12 of the pulse unit 4 so as to receivetorque impulses from a pulse generating mechanism 13 in the pulse unit 4. Thepulse unit 4 may e.g. be of the type described in EP 1747085 B1.The pulse tool 1 further comprises a motor angle sensor 7, such as an angle encoder, arranged to output data indicative of a rotation angle (angulardisplacement) output from the motor 3. Data indicative of the rotation angle maye.g. include the angular displacement itself or any parameter from which it is possible to derive such angular displacement, such as an angular position or angular velocity. The motor angle sensor 7 may e.g. be arranged so as to sense arotation angle of a component rigidly connected to (such as co-rotating with) therotor 6 of the motor. In the present example, the motor angle sensor 7 is arranged to sense the rotation of a support member 11 rigidly connected to theinertia drive member 5 of the pulse unit 4. The motor angle sensor 7 may e.g.comprise a rotating part 14 attached to the component co-rotating with themotor 3 (e.g. the support member 11) and a stationary part 15 arranged stationary in the housing of the tool 1. The rotating part 14 may comprise readable means that sensing means of the stationary part 15 can detect as they pass. The pulse tool 1 further comprises an output shaft angle sensor 8, such as an angle encoder, arranged to output data indicative of a rotation angle (angulardisplacement) of the output shaft 2. Data indicative of the rotation angle may e.g.include the angular displacement itself or any parameter from which it is possible to derive such angular displacement, such as an angular position or angular velocity. The output shaft angle sensor 8 may e.g. be arranged so as to sense a rotational displacement of a component rigidly connected to (such as co- rotating with) the output shaft 2. In the present example, the output shaft angle sensor 8 is arranged to sense the rotation of a support member 9 rigidly connected to the output shaft 2. The output shaft angle sensor 8 may e.g.comprise a rotating part 16 attached to the component co-rotating with theoutput shaft 2 (e.g. the support member 9) and a stationary part 17 arrangedstationary in the housing of the tool 1. The rotating part 16 may comprise readable means that sensing means of the stationary part 17 can detect as they pass. It will be appreciated that the motor angle sensor 7 and the output shaft sensor 8may be of any suitable type for outputting data indicative of a rotation angle,such as an optic or magnetic sensor. For example, they may be of the same typeas the angle encoder described in EP 1747085 B1 or as the displacement sensordescribed in WO 2014195424 A1.The pulse tool 1 may further comprise a control device 10. The control device 10may be communicatively connected to the angle sensors 7, 8. The control device 10 may comprise a memory and processing means. The control device 10 may be configured to receive the rotation angle data from the angle sensors 7, 8. The control device 10 may be configured to calculate the rotation angle (angulardisplacement) of the output shaft 2, preferably as counted from a predefinedstarting point (such as from a predetermined percentage of the target torque), based on the data from the motor sensor device 8.For example, the total output shaft displacement (rotation angle) φOtot (ascounted from a specific starting point) can be calculated by determining, at first,the total rotation angle φDtot output from the motor 3 (as indicated by the datafrom the motor sensor device 7) and then reducing that angle by the total angleφNtot of the total number of full revolutions: Ntot x 360°, minus one fullrevolution: 360°. This could be expressed: ^^^^^ = ^^^^^ − (^^^^ − 1) × 360One full revolution has to be deducted since the first pulse could be preceded byan unknown acceleration angle of the inertia drive member 5. Examples of howthe angle of the output shaft 2 can be calculated based on the data from themotor angle sensor 7 is described in more detail in EP 1747085 B1.The control device 10 may be configured to compare the calculated rotation angle of the output shaft 2 with the rotation angle as indicated by the data received from the output shaft angle sensor 8. The control device 10 may be configured to determine if these two rotation angles deviate from each other, such as by more than a predetermined number of degrees. In case these two rotation angles are found to deviate from each other, the control device 10 may be configured to take some kind of action. For example, the control device 10 may be configured to issue an alert to the operator. For example, a warning message may be issued indicating that one ofthe sensors 7, 8 is potentially deficient. The message may be displayed on adisplay of the tool 1 or on an external device connected to the tool 1. Alternatively (or additionally), the control device 10 may stop the ongoing tightening operation.Alternatively (or additionally), the control device 10 may disable the tool 1. Thismay include both interrupting an ongoing tightening and prevent a new tightening to be started. According to an embodiment, the control device 10 may be configured to determine a total angle of a tightening operation, preferably as counted from the predefined starting point. This total angle may preferably be determined basedon the data from the output shaft angle sensor 8 but may alternatively be basedon the data from the motor angle sensor 7. The control device 10 may thensave / send the total angle, e.g. together with the total torque of the tightening and other trace data of the tightening, to an assembly management system. Optionally, the pulse tool 1 may further comprise a gyro configured to sense an orientation / posture of the tool 1. The control device 10 may then base the determination of the rotation angle of the output shaft 2 also on data from the gyro so as to compensate for any movement of the tool 1 made by the operator during the tightening. Optionally, the control device 10 may be configured to determine a rundown angle of the tightening based on the data from the output shaft angle sensor 8. The correlation of the angle as indicated by the motor angle sensor 8 to the angle as indicated by the output shaft angle sensor 8 is unpredictable during rundown since the motor 3 and the output shaft 2 will co-rotate only as long as the torque is very low (close to zero), but as soon as just some torque is applied (e.g. due to some friction peak during rundown), the pulse unit 4 will operate, whereby the output shaft 2 will no longer co-rotate with the motor 3. Hence, a rundown angle may advantageously be determined based on data from the output shaft angle sensor 8. According to an embodiment, the angular data from the motor angle sensor 7 may be used as a basis for the control device 10 to estimate the torque applied to the fastener. Hence, no further torque transducer is required. The person skilled in the art realizes that the present invention by no means is limited to the embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the control device may, as an equivalent alternative to being comprised within the same housing as that of the motor, pulse unit and sensors, be comprised in a separate (optionally remote) housing (still in communication with the sensors). Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. 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. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that acombination of these measures cannot be used to advantage.

Claims

CLAIMS1. Pulse tool (1) for tightening joints, the pulse tool comprising:a motor (3);an output shaft (2);a pulse unit (4) arranged to be driven by the motor (3) and todeliver torque in pulses to the output shaft (2);a motor angle sensor (7) arranged to output data indicative of arotation angle output from the motor (3);an output shaft angle sensor (8) arranged to output data indicativeof a rotation angle of the output shaft (2); anda control device (10) configured to: -determine whether a rotation angle of the output shaft (2) ascalculated based on the data from the motor angle sensor (7) and arotation angle of the output shaft (2) as indicated by the data from theoutput shaft angle sensor (8) deviates from each other.

2. Pulse tool (1) as defined in claim 1, wherein the control device (10) isfurther configured to take measure in response to determining that therotation angle of the output shaft (2) as calculated based on the data from the motor angle sensor (7) and the rotation angle of the output shaft (2)as indicated by the data from the output shaft angle sensor (8) deviatesfrom each other more than to a predetermined extent.

3. Pulse tool (1) as defined in claim 1 or 2, wherein taking measurecomprises at least one of: issue an alert signal, interrupt the ongoing tightening operation and disable the pulse tool (1).

4. Pulse tool (1) as defined in any one of the preceding claims, wherein therotation angles are counted from a predetermined torque level.

5. Pulse tool (1) as defined in any one of the preceding claims, the controldevice (10) being configured to determine a total angle of a performedtightening based on the data from the output shaft angle sensor (8).

6. Pulse tool (1) as defined in any one of the preceding claims, the controldevice (10) being configured to estimate the torque applied to thefastener based on the data from the motor angle sensor (7).

7. Pulse tool (10) as defined in any one of the preceding claims,further comprising an orientation sensor arranged to sense an orientation of the pulse tool (1),the control device (10) being further configured to determine anangle of a tightening based on the data from the output shaft angle sensor(8) and data from the orientation sensor.

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