Method for detecting if a fastener is already tightened

Abstract

A method detects whether a fastener is already tightened using a tightening tool with a pulse mechanism. The method includes placing the tightening tool on the fastener, and accelerating rotational parts of the tightening tool. The rotational speed of the rotational parts is limited to a first rotational threshold value in revolutions per minute during an initial tightening phase, the first rotational threshold value being set to be in a range of 20% to 80% of a second rotational threshold value in revolutions per minute needed in a secondary tightening phase to provide a target fastening value for the fastener. And it is detected whether a pulse occurs during the initial tightening phase, the initial tightening phase being measured from a moment when the rotational parts are accelerated.

Claims

1. A method for detecting whether a fastener is already tightened, using a tightening tool with a pulse mechanism, the method comprising: placing the tightening tool on the fastener; accelerating rotational parts of the tightening tool; limiting a rotational speed of the rotational parts to a first rotational threshold value in revolutions per minute during an initial tightening phase, the first rotational threshold value being set to be in a range of 20% to 80% of a second rotational threshold value in revolutions per minute needed in a secondary tightening phase to provide a target fastening value for the fastener; detecting whether a pulse occurs during the initial tightening phase, the initial tightening phase being measured from a moment when the rotational parts are accelerated; and detecting that no pulse has occurred and accelerating the rotational parts of the tightening tool up to the second rotational threshold value in response to the detection that no pulse has occurred.

2. The method according to claim 1, further comprising: detecting that the pulse occurs, and detecting a torque value of the pulse.

3. The method according to claim 2, further comprising: determining that the torque value is at or above a predetermined torque threshold value, and aborting tightening in response to the determination.

4. The method according to claim 3, wherein the target fastening value is a target torque value, and wherein the predetermined torque threshold value is in a range of 7 Nm to 12 Nm.

5. The method according to claim 2, further comprising: determining that the torque value is below a predetermined threshold value, and accelerating the rotational parts of the tightening tool up to the second rotational threshold value in response to the determination.

6. The method according to claim 2, further comprising: signaling to an operator that the fastener is already tightened.

7. The method according to claim 1, wherein the initial tightening phase is measured in time and is in a range of 100 ms to 200 ms.

8. The method according to claim 7, wherein the initial tightening phase is in a range of 120 ms to 180 ms.

9. The method according to claim 8, wherein the initial tightening phase is in a range of 125 to 160 ms.

10. The method according to claim 1, wherein the initial tightening phase is measured in angle and is in a range of 180° to 1080°.

11. The method according to claim 10, wherein the initial tightening phase is in a range of 360° to 720°.

12. The method according to claim 11, wherein the initial tightening phase is in a range of 430° to 650°.

13. The method according to claim 1, wherein the first rotational threshold value is in a range of 800 revolutions per minute to 1200 revolutions per minute.

14. The method according to claim 13, wherein the first rotational threshold value is in a range of 900 to 1100 revolutions per minute.

15. The method according to claim 1, wherein the second rotational threshold value is in a range of 2000 revolutions per minute to 4000 revolutions per minute.

16. The method according to claim 15, wherein the second rotational threshold value is in a range of 2500 revolutions per minute to 3500 revolutions per minute.

17. The method according to claim 16, wherein the second rotational threshold value is in a range of 2800 revolutions per minute to 3200 revolutions per minute.

18. The method according to claim 1, wherein the target fastening value is a target torque value or target angle value.

19. The method according to claim 1, wherein the tightening tool is an electronic tightening tool, a pneumatic tightening tool, or a hydraulic tightening tool.

20. A tightening tool comprising: a pulse mechanism; a motor; a drive member; a measurement unit; and a processing unit connected to the measurement unit, wherein the motor is configured to drive the drive member, wherein the pulse mechanism is configured to rotate along with the drive member, wherein the measurement unit is configured to measure at least one of an angle, an applied torque, pulse, and time, and wherein the processing unit is configured to control the tightening tool to perform operations comprising: accelerating rotational parts of the tightening tool; limiting a rotational speed of the rotational parts to a first rotational threshold value in revolutions per minute during an initial tightening phase, the first rotational threshold value being set to be in a range of 20% to 80% of a second rotational threshold value in revolutions per minute needed in a secondary tightening phase to provide a target fastening value for a fastener; detecting whether a pulse occurs during the initial tightening phase, the initial tightening phase being measured from a moment when the rotational parts are accelerated; and accelerating the rotational parts of the tightening tool up to the second rotational threshold value if no pulse is detected.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will now be described, for exemplary purposes, in more detail by way of an embodiment and with reference to the enclosed drawings, in which:

(2) FIG. 1 schematically illustrates a tightening tool according to an embodiment of the present invention;

(3) FIG. 2a schematically illustrates a diagram illustrating the rotational speed development over time according to a known method;

(4) FIG. 2b schematically illustrates a diagram illustrating the rotational speed development over time using a method according to the invention;

(5) FIG. 2c schematically illustrates a diagram illustrating the rotational speed development over time under different circumstances than in FIG. 2b using the method according to the invention;

(6) FIG. 2d schematically illustrates a diagram illustrating the rotational speed development over time under again different circumstances than in FIGS. 2b and 2c using the method according to the invention; and

(7) FIG. 3 illustrates a flow chart of a method according to an embodiment of the present invention.

DETAILED DESCRIPTION

(8) FIG. 1 schematically illustrates an automatic tightening tool 1 comprising a housing 2 and power cable 3 connected to the housing 2. The housing 2 may comprise a handle 4 so that an operator can easily hold the tightening tool 1. In the housing 2 an electric transformer unit 5 connected to the power cable 3 is provided. The electric transformer unit 5 is connected to a measurement unit 6, which is connected to a processing unit 7. The processing unit 7 is connected to a motor 11 in order to control and power the motor 11. The motor 11 comprises a drive member 10, which drive member 10 again comprises a pulse mechanism 8, which pulse mechanism 8 is configured to rotate along with the drive member 10.

(9) The automatic tightening tool 1 is illustrated having a power cable 3, the present invention is however also suitable for battery-driven automatic tightening tools or automatic tightening tools powered by compressed air.

(10) The drive member 10 and the rotating parts of the motor 11 are the rotational parts of the tightening tool 10.

(11) The pulse mechanism 8 is connected to an output shaft 9, which output shaft 9 is configured to be connected to an adapter (not shown) or the like so that a fastener (not shown) can be coupled to the adapter and the output shaft 9, respectively.

(12) Although the output shaft 9 is configured to rotate in order to tighten fasteners, it is not considered to be part of the rotational parts herein.

(13) The processing unit 7 is configured and programmed to control the motor during the tightening of a fastener using the tightening tool 1. The measurement unit 6 is configured to measure the applied torque through the output shaft 9 and the angle of rotation of the output shaft 9 and the rotational parts 10, 11, respectively. Depending on the tightening phase and the state of the fastener the output shaft the processing unit 7 is configured to abort the tightening, if it is detected that the fastener is already tightened with a torque value corresponding to or above predetermined torque threshold value or accelerate the rotational parts to tighten the fasteners as specified if the torque value is below the predetermined torque threshold value. The torque value is monitored and measured via the measurement unit 6.

(14) For the pulse mechanism 8 to work and actually apply pulses of a certain torque to the output shaft 9 a certain rotational speed of motor 11 and the drive member 10, respectively, is required. In other words the speed of rotation of the rotational parts 10, 11 defines what torque or angle can be applied to the fastener via the output shaft 9.

(15) The electric transformer unit 5, the measurement unit 6, the processing unit 7, the motor 11, the drive member 10 and the pulse mechanism 8 are illustrated in dashed lines in FIG. 1, since they are embedded in the housing 2 and thus not directly visible. These units are shown for illustrative purposes.

(16) In order to better understand the tightening of a fastener and the method according to the present invention it is now referred to FIGS. 2a to 2d.

(17) FIGS. 2a to 2d illustrate the course or development of the rotational speed during a tightening of a fastener or bolt over time. The rotational speed (RPM) is illustrated on the left y-axis while the x-axis illustrates the time passed, typically in milliseconds.

(18) FIGS. 2a to 2d illustrate various situations that can occur during a tightening of a fastener, whereby FIG. 2a illustrate a known technique according to the prior art. The rotational speed may be measured directly on a drive axle of the motor 11 or in the pulse mechanism 8. It is to be noted that the rotational speed measured at the drive axle or in the pulse mechanism 8 does not need to correspond to the rotational speed of the output shaft 9.

(19) FIG. 2a illustrates a rotational speed development over time of the rotational parts of an automatic tightening tool using a previously known method. FIG. 2a shows how the rotational speed develops over time when a fastener that has not been tightened previously up to a target fastening value T2 is tightened. The rotational parts 10, 11 are accelerated and torque or angle movement/rotation is applied to the fastener in order to tighten a joint. Once resistance occurs during the tightening the speed of the rotational parts will drop abruptly and the pulse mechanism 8 will initiate a pulse P1 with a certain fastening value (illustrated as dashed lines in FIG. 2a), typically below the target fastening value T2. After the first pulse P1 the rotational parts are accelerated again to generate a second pulse P2 with a higher fastening value than the first pulse P1 but still below the target fastening value T2 and so on.

(20) The fastening value peaks or torque value peaks are indicated in the FIGS. 2a to 2d with dashed lines for illustrative purposes. They occur whenever a pulse (P1, P2) occurs and the rotational speed drops to zero or at least close to zero. After the target fastening value T2 is reached the tightening is finished and stopped.

(21) In FIG. 2a an initial tightening phase ITP is illustrated, whereby this is only done in order to properly compare FIGS. 2b to 2d with FIG. 2a. In FIG. 2a the initial tightening phase is not of interest. In the method according to FIG. 2a the rotation of the rotational parts is accelerated up to a second rotational threshold value R2, which is needed to tighten a fastener according to a specification and according to a target fastening value T2. FIG. 2a illustrates the normal case where a fastener that has not been previously tightened, is tightened. When a fastener that has been tightened already is tightened again using the known method according to FIG. 2a by accelerating the rotational parts immediately up to the second rotational threshold value R2, then the risk is high that the first pulse (not shown) or any subsequent pulse generates a fastening value or torque that is above the target fastening value T2 for said fastener and thereby generates a tightened fastener that cannot be approved since it is tightened with a higher value/torque than specified.

(22) As mentioned, if the same procedure or known method illustrated in FIG. 2a is applied to an already tightened fastener the risk is high that such an already tightened fastener is tightened above the target fastening value T2, since the processing unit 7 will accelerate the motor 11 and drive member 10 directly and almost immediately up to a second rotational threshold value R2, which is needed to apply the target fastening value T2. In view of this a first rotational threshold value R1 (FIGS. 2b-2d) corresponding to a predetermined torque threshold value T1 is introduced.

(23) FIG. 2b illustrates the rotational speed development of the rotational parts thus the motor and drive member 10 when an untightened fastener is tightened using the method according to the invention. In FIG. 2b it is well visible, that a first rotational threshold value R1 is introduced, said first rotational threshold value R1 being used to limit the applied torque during pulses occurring in the initial tightening phase ITP. As can be seen from FIG. 2b there is no pulse occurring during the initial tightening phase ITP and therefore after the initial tightening phase the rotational parts are accelerated up to the second rotational threshold value R2 and the tightening proceeds as previously explained referring to FIG. 2a until the target fastening value T2 is reached. FIG. 2b illustrates the normal case using the method according to the present invention.

(24) FIG. 2c illustrates the tightening of a fastener when the fastener is not previously tightened but a pulse P1′ occurs anyway during the initial tightening phase ITP. This can happen when there is dirt in the thread or when joint has parts with various stiffness. It has to be noted that the pulse P1′ needs to be at least detectable. The measurement unit 6 then determines the torque value of the pulse P1′ that occurred during the ITP. If the torque value (dashed line of first pulse P1′) of the pulse P1′ is below the predetermined torque threshold value T1, then it is assumed that the fastener has not been previously tightened. In FIG. 2c the torque value of the pulse P1′ is comparably weak and below the predetermined torque threshold value T1 and therefor the tightening tool 1 and the processing unit 7, respectively, will increase the rotational speed up to the second rotational threshold limit R2 in order to tighten the fastener up to the specified target fastening value T2 and tighten the fastener as described referring to FIG. 2a. Alternatively the fastener may be tightened to the target fastening value T2 by keeping the rotational parts of the first rotational threshold value R1, this is however not shown in FIG. 2c. It is to be noted that the value of the predetermined torque threshold value T1 is only illustrated for understanding purposes the diagram only shows rotational speed versus time.

(25) FIG. 2d illustrates the situation when an actual “rehit” occurs, thus when an already tightened fastener is connected to the automatic tightening tool and tried to be tightened again. As can be seen from FIG. 2d a pulse P1″ also occurs during the initial tightening phase ITP whereby the value or torque value of this pulse P1″ is determined by the measuring unit 6. The value of the torque of this pulse P1″ is illustrated to be above (or corresponding to for that matter) to the predetermined torque threshold value T1. This leads to the conclusion that the fastener has been previously tightened due to the occurrence of a strong pulse P1″ generating a torque corresponding to or above the predetermined torque threshold value T1. The tightening will thus be aborted and stopped. This can be signaled to the user.

(26) FIG. 3 illustrates the method steps according to an embodiment of the invention. The method comprises the steps of: placing S01 the tightening tool 1 on the fastener; accelerating S02 the rotational parts 10, 11 of the tightening tool 1; limiting S03 a rotational speed of the rotational parts 10, 11 to a first rotational threshold value R1 in revolutions per minute during an initial tightening phase ITP, the first rotational threshold value R1 being chosen to be in a range of 20% to 40% or 20% to 80%, or 30% to 80% or 40% to 80%, of a second rotational threshold value R2 in revolutions per minute needed in a secondary tightening phase to provide a target fastening value T2 for said fastener; and detecting S04 whether a pulse P1, P2, P1′, P1″ occurs during the initial tightening phase ITP, said initial tightening phase ITP being measured from a moment when the rotational parts 10, 11 are accelerated up to a certain length measured in time.

(27) The above steps S01 to S04 can theoretically already allow to determine if the fastener has been previously tightened or not. It may be decided based on the presence of a pulse P1, P2, P1′, P1″ that the fastener has been previously tightened thus a pulse P1, P2, P1′, P1″ was detected S04 or that the fastener has not been previously tightened thus no pulse P1, P2, P1′, P1″ was detected.

(28) In particular if the joints with consistent friction and variable stiffness are tightened the presence of a pulse P1, P2, P1′, P1″ can be enough to decide/assume that the joint has been previously tightened.

(29) If no pulse P1, P2, P1′, P1″ is detected, step S05, then the rotational parts 10, 11 are accelerated S07 up to the second rotational threshold value R2 corresponding to a target fastening value T2 for tightening the fastener up to the target fastening value T2.

(30) If a pulse P1, P1′ is detected in the initial tightening phase ITP, during step S05, then the torque value of the pulse P1, P1′ is determined S06 and if the torque value is corresponding to or above a predetermined torque threshold value T1 then tightening is aborted S09. If the torque value of the pulse P1, P1′ is below the predetermined torque threshold value T1, then the rotational parts 10, 11 may be accelerated S07 up to a second rotational threshold value R2 in order to provide the target fastening value T2, as described above. This further acceleration up to the second rotational threshold value R2 also marks the beginning of a secondary tightening phase which follows the initial tightening phase ITP. The secondary tightening phase will only happen if no pulse or a pulse with a torque value below the predetermined torque threshold value T1 is present. The stop or abortion S09 of the tightening can be signaled S10 to the operator, this can be done visually, tactile or through a sound signal.

(31) In the following some exemplary values are given for the various thresholds:

(32) The initial tightening phase ITP is measured as a time period and it may be in the range of 100 ms to 200 ms, preferably in the range of 120 ms to 180 ms and more preferably in the range of 125 to 160 ms, whereby ms are milliseconds. The initial tightening phase ITP is measured from the moment the acceleration of the rotational parts 10, 11 up to the first rotational threshold value R1 starts.

(33) Alternatively to the above the initial tightening phase ITP is measured in angle of rotation of the rotational parts and is in the range of 180° to 1080°, preferably 360° to 720° and more preferably 430° to 650°.

(34) The target fastening value T2 can correspondingly to the above be a target torque value T2 and the predetermined torque threshold value T1 is typically in a range of 7 Nm to 12 Nm, preferably 8 to 11 Nm and more preferably 8.5 Nm to 10 Nm, whereby Nm is Newton meter. It is however clear to the skilled person that these values are not absolute. Different applications and joints may require higher or lower torque values.

(35) The predetermined torque threshold value T1 is typically in a range of 10% to 50% of the target fastening value/target torque value T2, preferably 15% to 25% of the target fastening value/target torque value T2.

(36) Alternatively to the above the target fastening value T2 is an angle, which tightens the joint and fastener, respectively according to the specification. This may be the case if an angle controlled device is used.

(37) The first rotational threshold value T1 is in the range of 800 revolutions per minute to 1200 revolutions per minute, preferably about 900 to 1100 revolutions per minute.

(38) The second rotational threshold value is in the range of 2000 revolutions per minute to 4000 revolutions per minute, preferably about 2500 revolutions per minute to 3500 revolutions per minute and more preferably about 2800 revolutions per minute to 3200 revolutions per minute.

(39) As mentioned the given values above are examples for a torque environment of approximately 20 Nm to 55 Nm. The method can however be applied and scaled to other torque environments that are higher or lower as the given examples. The method is thus in no way limited to a specific torque environment.