Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
  • B25B—TOOLS OR BENCH DEVICES NOT OTHERWISE PROVIDED FOR, FOR FASTENING, CONNECTING, DISENGAGING OR HOLDING
  • B25B21/00—Portable power-driven screw or nut setting or loosening tools; Attachments for drilling apparatus serving the same purpose
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
  • B25B—TOOLS OR BENCH DEVICES NOT OTHERWISE PROVIDED FOR, FOR FASTENING, CONNECTING, DISENGAGING OR HOLDING
  • B25B23/00—Details of, or accessories for, spanners, wrenches, screwdrivers
  • B25B23/14—Arrangement of torque limiters or torque indicators in wrenches or screwdrivers
  • B25B23/142—Arrangement of torque limiters or torque indicators in wrenches or screwdrivers specially adapted for hand operated wrenches or screwdrivers
  • B25B23/1422—Arrangement of torque limiters or torque indicators in wrenches or screwdrivers specially adapted for hand operated wrenches or screwdrivers torque indicators or adjustable torque limiters
  • B25B23/1425—Arrangement of torque limiters or torque indicators in wrenches or screwdrivers specially adapted for hand operated wrenches or screwdrivers torque indicators or adjustable torque limiters by electrical means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
  • B25B—TOOLS OR BENCH DEVICES NOT OTHERWISE PROVIDED FOR, FOR FASTENING, CONNECTING, DISENGAGING OR HOLDING
  • B25B23/00—Details of, or accessories for, spanners, wrenches, screwdrivers
  • B25B23/14—Arrangement of torque limiters or torque indicators in wrenches or screwdrivers
  • B25B23/147—Arrangement of torque limiters or torque indicators in wrenches or screwdrivers specially adapted for electrically operated wrenches or screwdrivers

Definitions

• the invention relates to a method of performing a tightening operation by means of a handheld power wrench with a first and a second angular measuring device.
• the invention also relates to a power tool adapted to perform said method.
• Modern professional power wrenches are provided with a number of sensors and means for detecting and reporting parameters of on-going and performed tightening operations .
• Parameters that may be detected and reported include the applied torque, the installed angular increment of a bolt, screw or nut of a joint and in some instances the clamp force installed into the joint.
• WO 2015/139952 Al discloses a method of obtaining a high clamp force accuracy in a threaded joint mounting process.
• a gyro or the like is used to monitor the clamp force installed into a joint.
• the gyro is used to monitor the angle of the tool, which is recalculated to a clamp force.
• the clamp force is a parameter that is relevant in many tightening operations, but in some operations other parameters may however be more interesting and more easily monitored.
• a method that provides an improved accuracy for tightening operations, but which offers an alternative to a method in which the operation is governed based on the clamp force installed into a joint.
• An object of the invention is to provide a method of performing an operation of tightening a joint with an increased accuracy.
• an object of the invention is to provide an accurate monitoring of the installed angle of a handheld torque delivering power tool without the use of torque arms or other means for
• this object is achieved by means of a method of tightening a joint by means of a handheld torque delivering power tool, the power tool comprising:
• a first angular measuring device for monitoring the angle of rotation of the output shaft about the axis of the output shaft with respect to the housing
• a second angular measuring device arranged to monitor angle of rotation of the housing around the axis of the output shaft relative to the surrounding area
• the invention relates to a handheld torque delivering power tool comprising:
• a first angular measuring device for monitoring the angle of rotation of the output shaft about the axis of the output shaft with respect to the housing
• a second angular measuring device arranged to monitor angle of rotation of the housing around the axis of the output shaft relative to the surrounding area
• control unit wherein the control unit is arranged to perform the following steps:
• a yield tightening is performed, which indicates that a plastic deformation of the fastener in the joint is achieved.
• the step of interrupting the tightening operation is preceded by a step of identifying the appearance of a substantially linear torque per angle coefficient and registering a linear gradient that corresponds to the substantially linear torque per angle of rotation, wherein the predetermined stop gradient is set in relation to said linear gradient.
• This step is in the power tool achieved by the control unit.
• the tightening operation is interrupted at a point where the instantaneous differential coefficient of the monitored torque per monitored angle of the output shaft relative to the surrounding area has reached below 90% of the linear gradient, or 75% of the linear gradient. This step may also be achieved by the control unit.
• Fig. 1 is a diagram of the dependency of the torque T with respect to an angle a of an output shaft during a tightening operation
• Fig. 2 shows a power tool in an initial position
• Fig. 3 shows a power tool in an position where both the tool housing and output shaft have rotated with respect to the axis of the output shaft
• Fig. 4 shows the steps of the inventive method. Detailed description of the shown embodiment of the invention
• Fig. 1 shows a diagram of the dependency of the torque T that is installed into a joint with respect to an angle a by which a fastener of the joint is rotated.
• the curve represents a typical curve of a tightening operation in which the joint is tightened into the yield area, i.e. such that a plastic deformation of the fastener is achieved.
• the torque is constant during a first period in which the fastener is rotated towards the joint, i.e.
• the tightening operation may be set to be interrupted when the differential coefficient reaches a predetermined stop
• the predetermined stop gradient k st o P at which the tightening should be interrupted may be set in relation to a specific fraction of the linear gradient ki in the linear portion, i.e.
• the gradient must however be a compromise between the need to interrupt the tightening before the fastener risks to rupture and the need to be sure that the plastic deformation has actually started .
• the predetermined stop gradient k s to P at which the tightening should be interrupted differs too little from the linear gradient ki of the linear portion the tightening operation may be interrupted prematurely due to a natural variation or a tolerance fault. If, on the other hand, the predetermined stop gradient k s to P is set too high the risk of rupture of the fastener will increase.
• the predetermined stop gradient k stop may be tested by a skilled person, and may
• the tightening operation may e.g. be set to be interrupted when the instantaneous differential coefficient dT/da has reached below 75% or 90% of the linear gradient ki .
• the angle at which the tightening operation is interrupted may be defined as a s to P and the corresponding torque at which the tightening operation is interrupted may be defined as T s to P , even though the operation is not controlled towards a specific angle nor a specific torque but to the
• Another feature concerned with a yield tightening is to prepare for the interruption in advance such that the targeted the predetermined stop gradient k st o P is met.
• special care has to be taken to the movement of the tool .
• Figures 2 and 3 show a power tool in two different positions.
• the power tool is illustrated in an initial position and in figure 3 the power tool is shown in an off-set position in which the output shaft has rotated about the axis of the output shaft with respect to the housing with an angle a , and in which the housing has rotated around the axis of the output shaft relative to the
• the combined angle a is hence the sum of a and (3 ⁇ 4 and corresponds to the rotation of a fastener with respect to a joint, the joint being fixed with respect to the surrounding area.
• 105 Calculating a differential coefficient of the monitored torque per monitored angle; 106 -Identifying an installed clamp force, e.g. by identifying the appearance of a substantially linear torque per angle coefficient;
• Step 106 may be omitted and in such a case step 107 will be defined in an absolute number, i.e. as a specific predetermined decrease of the torque per angle coefficient and not in relation to the substantially linear torque per angle coefficient.
• the power tool 10 is provided with an output shaft 11, which is to be connected to and drive the rotation of a fastener, and a handle 12 at which the power tool is to be held by an operator.
• the power tool may also be provided with a second handle for positioning of the operator's other hand.
• a motor 13 and preferably a gear (not shown) is arranged to drive the output shaft .
• a housing 14 is arranged to house the motor 13, gears and other features, such as a first angular measuring device 15, a second angular measuring 16 device torque monitoring device 17 and a control unit 18.
• the first angular measuring device 15 is arranged to monitor the angle of rotation a of the output shaft 11 about the axis of the output shaft with respect to the housing 14.
• the second angular measuring device 16 is arranged to monitor the angle of rotation (3 ⁇ 4 of the housing 14 around the axis of the output shaft 11 relative to the surrounding area.
• the torque monitoring device 17 is arranged to monitor the torque T during a tightening operation .
• a control unit 18 is arranged in the power tool to control the operation of the tool based on the monitored torque T and angles of rotation a and
• control unit 18 an instantaneous differential coefficient dT/da of the monitored torque T per monitored angle a of the output shaft 11 relative to the surrounding area is calculated.
• the control unit 18 is arranged to instruct the motor 13 to interrupt the tightening
• the decrease may be defined in absolute numbers or as fraction of the differential coefficient ki in the linear portion of the curve shown in figure 1.
• angles a n defined in the diagram are all the sum of the angles a a and ab provided by the first and second angular measuring device 15 and 16, respectively.
• ai corresponds to the sum of the individually monitored angles a a -i and oib-i ⁇
• a 2 a a -2 + a b -2
• a s to P a a - s to P + a b -sto P .

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Details Of Spanners, Wrenches, And Screw Drivers And Accessories (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=58018089

Family Applications (1)

Country Status (2)

Family Cites Families (5)

• 2017
  • 2017-02-09 EP EP17704723.0A patent/EP3419789A1/de not_active Withdrawn
  • 2017-02-09 WO PCT/EP2017/052849 patent/WO2017144281A1/en active Application Filing

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