ELECTRIC TOOL ADAPTED TO PERFORM TIGHTENING OPERATIONS WHERE TORQUE IS DELIVERED IN PULSES

Abstract

An electric tool adapted to perform tightening operations where torque is delivered in pulses to tighten a screw joint. The electric tool including an electric motor drivingly connected to an output shaft. A processor and a memory storing software instructions that, when executed by the processor cause the electrical tool, retrieve a first power level parameter p1 indicating a first power level to be used for torque pulses up to a torque threshold. And retrieve a second power level parameter p2 indicating a second power level to be used for torque pulses above the torque threshold. Then control the speed of the electric motor, so that the electric tool provide torque pulses on the output shaft with the first power level p1 until the torque threshold is reached. And control the speed of the electric motor, so that the electric tool provide torque pulses on the output shaft with the second power level p2.

Claims

1.-9. (canceled)

10. An electric tool adapted to perform tightening operations where torque is delivered in pulses to tighten a screw joint, the electric tool comprising: an electric motor drivingly connected to an output shaft, wherein the pulses are provided by a hydraulic pulse unit coupled to the electric motor, the hydraulic pulse unit intermittently couples the electric motor via a hydraulic coupling mechanism to the output shaft, or wherein the speed of the electric motor is controlled so that the electric motor is driven in a pulsed manner to provide pulses on the output shaft, the electric tool further comprising a processor; and a memory storing software instructions that, when executed by the processor cause the electrical tool to: retrieve at least first power level parameter p1 indicating a first power level to be used for torque pulses up to a torque threshold; retrieve at least a second power level parameter p2 indicating a second power level to be used for torque pulses above the torque threshold; retrieve the torque threshold indicating the torque up to which the first power level should be used; control the speed of the electric motor, so that the electric tool provides torque pulses on the output shaft with the first power level p1 until the torque threshold is reached; and control the speed of the electric motor, so that the electric tool provides torque pulses on the output shaft with the second power level p2.

11. The electric tool according to claim 10, wherein the first and second power level parameters p1 and p2 are expressed as percentage of the maximum power level.

12. A method for controlling an electric tool where tightening operations are performed by delivering pulses to tighten a screw joint, the electric tool comprising: an electric motor drivingly connected to an output shaft, wherein the pulses are provided by a hydraulic pulse unit coupled to the electric motor, the hydraulic pulse unit intermittently couples the electric motor via a hydraulic coupling mechanism to the output shaft, or wherein the speed of the electric motor is controlled so that the electric motor is driven in a pulsed manner to provide pulses on the output shaft, the method comprising the steps of: retrieving at least first power level parameter p1 indicating a first power level to be used for torque pulses up to a torque threshold; retrieving at least a second power level parameter p2 indicating a second power level to be used for torque pulses above the torque threshold; retrieving the torque threshold indicating the torque up to which the first power level should be used. controlling the speed of the electric motor, so that the electric tool provides torque pulses on the output shaft with the first power level p1 until the torque threshold is reached; and controlling the speed of the electric motor, so that the electric tool provides torque pulses on the output shaft with the second power level p2.

13. The method according to claim 12, wherein the first and second power level parameters p1 and p2 are expressed as percentage of the maximum power level.

14. A computer readable storage medium storing software instructions which causes an electrical tool to perform tightening operations where torque is delivered in pulses to tighten a screw joint, the electric tool comprising: an electric motor drivingly connected to an output shaft, wherein the pulses are provided by a hydraulic pulse unit coupled to the electric motor, the hydraulic pulse unit intermittently couples the electric motor via a hydraulic coupling mechanism to the output shaft, or wherein the speed of the electric motor is controlled so that the electric motor is driven in a pulsed manner to provide pulses on the output shaft, and wherein when the software instructions are executed by the processor cause the electrical tool to: retrieve at least a first power level parameter p1 indicating a first power level to be used for torque pulses up to a torque threshold; retrieve at least a second power level parameter p2 indicating a second power level to be used for torque pulses above the torque threshold; retrieve the torque threshold indicating the torque up to which the first power level should be used; control the speed of the electric motor, so that the electric tool provides torque pulses on the output shaft with the first power level p1 until the torque threshold is reached; and control the speed of the electric motor, so that the electric tool provides torque pulses on the output shaft with the second power level p2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention will now be described in more detail and with reference to the accompanying drawings, in which:

[0019] FIG. 1 shows a longitudinal section through the electric tool according to an exemplary embodiment of the present disclosure.

[0020] FIG. 2 shows example diagram of torque pulses according to an exemplary embodiment of the present disclosure.

[0021] FIG. 3 illustrates a flow chart according to an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

[0022] Aspects of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings. The device, method and computer program disclosed herein can, however, be realized in many different forms and should not be considered as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout.

[0023] The terminology used herein is for the purpose of describing particular aspects of the disclosure only, and is not intended to limit the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0024] FIG. 1 depicts an exemplary embodiment of an electric tool 10 in accordance with an embodiment of the present disclosure. The electric tool 10 further comprising a front end 10a and a back end 10b. The electric tool 10 further comprises a motor 12. The motor 12 comprising a rotor 14 that is arranged to rotate with respect to a stator 13. An output shaft 16 is arranged at the front end 10a of the housing 10. The electric tool 10, according to the illustrated embodiment, further comprises a hydraulic pulse unit 15 which is coupled to the electric motor 12. The hydraulic pulse unit 15 intermittently couples the inertia drive member 18 via a hydraulic coupling mechanism to the output shaft 16. The function of a hydraulic pulse unit 15 is well known to a person skilled in the art and is not described in detail in this application. A more detailed description of the function of a pulse unit is described in the international patent application WO 91/14541.

[0025] The electric tool 10 further comprise a processor 20 arranged to control the electric motor 12. The electric tool 10 also comprises a memory 26 containing instructions executable by the processor 20.

[0026] The inventor has realised that higher accuracy and faster tightening can be achieved by allowing the user to set the power of the pulses for different stages of the tightening.

[0027] An advantage with this solution is that the power can be set to be optimized during different stages of the tightening to achieve high accuracy and speed. Thus one aspect of the present disclosure relates to an electric tool where the memory 26 containing instructions which when run in the electrical pulse tool causes the electrical tool to control the speed of the electric motor 12, so that the electric tool 10 provide torque pulses on the output shaft 16 with the first power level p1 until the torque threshold is reached.

[0028] According to one exemplary embodiment the electric tool comprises an angle sensor (not shown) arranged to determine the position of the motor 12. According to one exemplary embodiment the angle sensor is positioned between the motor 12 and the inertia drive member 18. The angle senor can however be located on other places in the electric tool.

[0029] According to one exemplary embodiment the power of the pulses are determined by providing a current to the electric motor 12 during a predetermined time interval. According to another exemplary embodiment the power of the pulses are provided by providing a current to the electric motor 12 during a predetermined time interval and at the same time monitor the speed of the motor 12. By providing a current to the electric motor 12 during a predetermined current on time interval and at the same time monitor the speed of the motor 12 a certain determined power can be achieved. If a desired power is not reached at a certain angle of the motor 12, a new current pulse can be provided to the motor 12. This in order to make sure that the desired power of the motor is obtained at the moment the motor 12 couples to the output shaft 16.

[0030] According to another exemplary embodiment the power is constantly measures and the current feed is controlled so that the power is reached at the moment the inertia drive member 18 couples to the output shaft 16 and the pulse is provided to the screw being tightened. According to yet another exemplary embodiment the power of the motor 12 is controlled by continuously monitor the actual position of the motor 12 and take the position into account when determining the power.

[0031] Referring back to FIG. 1, the processor 20 is a Central Processing Unit, CPU, microcontroller, Digital Signal Processor, DSP, or any other suitable type of processor capable of executing computer program code. The memory 26 is a Random Access Memory, RAM, a Read Only Memory, ROM, or a persistent storage, e.g. a single or combination of magnetic memory, optical memory, or solid state memory or even remotely mounted memory.

[0032] According to one aspect, the disclosure further relates to the above mentioned computer program, comprising computer readable code which, when run on the electric tool causes the electric tool to perform any of the aspects of the disclosure described herein.

[0033] According to one aspect of the disclosure the processor 20 comprises one or several of: [0034] a retrieve module 161 adapted retrieve at least first power level parameter p1 indicating a first power level to be used for torque pulses up to a torque threshold, retrieve at least a second power level parameter p2 indicating a second power level to be used for torque pulses above the torque threshold and retrieve the torque threshold indicating the torque up to which the first power level should be used; [0035] a control module 162 adapted control the speed of the electric motor 12, so that the electric tool 10 provide torque pulses on the output shaft 16 with the first power level p1 until the torque threshold is reached and control the speed of the electric motor 12, so that the electric tool 10 provide torque pulses on the output shaft 16 with the second power level p2.

[0036] The control modules 161 and 162 are implemented in hardware or in software or in a combination thereof. The modules 161 and 162 are according to one aspect implemented as a computer program stored in the memory 26 which run on the processor 20. The electric tool is further configured to implement all the aspects of the disclosure as described herein.

[0037] Now turn to FIG. 2, which shows one example of a number of pulses in a tightening performed by the electric tool 1 according to the present disclosure. FIG. 2 comprises three graphs. The graph at the top illustrates the power of the pulses. The graph in the middle illustrates the target torque for the tightening. And the graph at the bottom illustrates the torque t (pulse torque) of the pulses n. As can be seen in the top graph of FIG. 2, the power of the pulses vary during the tightening.

[0038] In the illustrated tightening the power of the pulses in the beginning are low. The electric tool provides torque pulses on the output shaft 16 with the first power level p1, since the torque threshold has not been reached.

[0039] Then the power level of the pulses increases since the torque threshold has been reaches and the user has set the power level to a higher value after the torque threshold. As the torque of the pulses get closer to the target torque, the power of the pulses decreases since the user has set the power of the pulses to an even lower value in order to reach the target torque with good accuracy.

[0040] As can be seen from FIG. 2, the electric tool is operative to repeat the pulses until a parameter value associated with the tightening of a screw joint has been reached. In an exemplary embodiment of the electric tool the parameter value associated with the tightening of a screw joint is torque. In yet another exemplary embodiment of the electric tool the parameter value associated with the tightening of a screw joint is angle.

[0041] The present disclosure also relates to a computer-readable storage medium, having stored there on a computer program which, when run in the electrical pulse tool, causes the electrical pulse tool to be operative as described above.

[0042] According to one exemplary embodiment, when the above-mentioned computer program code is run in the processor 20 of the electric tool it causes the electric tool to be operative as described above.

[0043] FIG. 3 illustrates a flow chart of a method for controlling an electric tool where tightening operations are performed by delivering pulses to tighten a screw joint. The electric tool 10 comprising an electric motor 12 drivingly connected to an output shaft 16. The method comprising a step 110 of retrieving at least first power level parameter p1 indicating a first power level to be used for torque pulses up to a torque threshold. In a step 120, retrieve at least a second power level parameter p2 indicating a second power level to be used for torque pulses above the torque threshold. Next in a step 130, retrieve the torque threshold indicating the torque up to which the first power level should be used. Thereafter in a step 140, control the speed of the electric motor 12, so that the electric tool 10 provide torque pulses on the output shaft 16 with the first power level until the torque threshold is reached. Then, in a step 150, control the speed of the electric motor 12, so that the electric tool 10 provide torque pulses on the output shaft 14 with the second power level p2.

[0044] According to another exemplary embodiment, wherein the first and second power level parameters p1 and p2 are expressed as percentage of the maximum power level. In another exemplary embodiment of the method, the pulses are provided by a hydraulic pulse unit 13 coupled to the electric motor 12, the hydraulic pulse unit 15 intermittently couples the electric motor 12 via a hydraulic coupling mechanism to the output shaft 16. In another exemplary embodiment of the speed of the electric motor 12 is controlled so that the electric motor is driven in a pulsed manner to provide pulses on the output shaft 16.