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EP-4735207-A1 - CONTROLLING A MOTOR OF A PULSE TOOL USING UPPER AND LOWER LIMITS

EP4735207A1EP 4735207 A1EP4735207 A1EP 4735207A1EP-4735207-A1

Abstract

A method of controlling a motor of a pulse tool is provided. The method comprises: determining a parameter value indicative of a torque and/or angle increase achieved by a just performed pulse (n); determining a motor power control parameter value (M) for the next pulse (n+1) based on said determined parameter value (d) indicative of the torque and/or angle increase and such that said motor power control parameter value is kept between an upper limit (M max ) and a lower limit (M min ); controlling the motor according to the determined motor power control parameter value to create the next pulse. Further, the upper and lower limits are set so as to converge towards a predetermined final target window (M w ) defining an allowable range within which the motor power control parameter value for the last pulse of the tightening operation is to be comprised. Thereby, less spread in installed torque is provided.

Inventors

  • FRIBERG, Christian

Assignees

  • Atlas Copco Industrial Technique AB

Dates

Publication Date
20260506
Application Date
20240530

Claims (15)

  1. 1. Method (400) of controlling a motor (12, 112) of a pulse tool (1, 101), the pulse tool being arranged to provide torque in pulses during a tightening operation to tighten a threaded joint, the method comprising: - determining (402) a parameter value (d) indicative of a torque increase and/or angle increase achieved by a just performed pulse (n); - determining (403) a motor power control parameter value (M) for the next pulse (n+1) based on said determined parameter value indicative of the torque increase and/or angle increase and such that said motor power control parameter value is kept between an upper limit (M max ) and a lower limit (M m m); - controlling (404) the motor according to the determined motor power control parameter value to create the next pulse; and repeating these steps until a target torque and/or angle is reached, wherein the upper and lower limits are set so as to converge towards a predetermined final target window (M w ) defining an allowable range within which the motor power control parameter value for the last pulse of the tightening operation is to be comprised.
  2. 2. Method according to claim 1, wherein the final target window is predetermined based on the target torque for the tightening operation.
  3. 3. Method according to claim 1 or 2, wherein the final target window is predetermined based on the characteristics of the pulse tool.
  4. 4. Method according to any one of the preceding claims, wherein the width of the final target window corresponds to less than 40% of a maximum output specified for the motor, such as less than 30% of a maximum output specified for the motor, such as less than 20% of a maximum output specified for the motor.
  5. 5. Method according to any one of the preceding claims, wherein determining said parameter value indicative of the torque increase and/or angle increase comprises determining a difference (d) between a received input indicative of a torque and/or angle achieved in the just performed pulse and a received input indicative of a torque and/or angle achieved in the pulse (n-1) just before the just performed pulse.
  6. 6. Method according to any one of the preceding claims, further comprising, before the tightening operation starts, receiving (401) input indicative of a desired trade-off between speed and accuracy of the tightening operation.
  7. 7. Method according to claim 6, wherein the upper and lower limits and/or the width of the final target window are based on said received input indicative of the desired trade-off between speed and accuracy.
  8. 8. Method according to any one of the preceding claims, wherein the motor power control parameter value for the next pulse is determined to be lower with a larger torque increase and/or smaller angle increase as indicated by said determined parameter value, and higher with a smaller torque increase and/or larger angle increase as indicated by said determined parameter value.
  9. 9. Method according to any one of the preceding claims, wherein the motor power control parameter is any one of: motor power, motor current, motor torque, energy output from the motor, and motor speed.
  10. 10. Method according to any one of the preceding claims, wherein the pulses are provided by a hydraulic pulse unit (15) of the pulse tool (1), wherein the hydraulic pulse unit intermittently couples the motor (12) via a hydraulic coupling mechanism to an output shaft (16) of the pulse tool.
  11. 11. Method according to any one of claims 1 to 9, wherein the motor (112) is driven in a pulsed manner to provide the pulses on an output shaft (116) of the pulse tool (101), wherein the output of the motor zero between the pulses.
  12. 12. Control device (20) for controlling a motor of a pulse tool, the pulse tool being arranged to provide torque in pulses during a tightening operation to tighten a threaded joint, the control device being configured to perform the method according to any one of the preceding claims.
  13. 13. System comprising: a pulse tool arranged to provide torque in pulses during a tightening operation to tighten a threaded joint, the pulse tool comprising a motor; and a control device according to claim 12 for controlling the motor of the pulse tool.
  14. 14. Computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method as defined in any one of claims 1-11.
  15. 15. Computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the method as defined in any one of claims 1-11.

Description

CONTROLLING A MOTOR OF A PULSE TOOL USING UPPER AND LOWER LIMITS Field of the invention The present invention generally relates to the field of controlling motors of pulse tools. In particular, the present invention relates to pulse strategies for such pulse tools. 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 either by means of a hydraulic pulse unit that intermittently couples the motor to the output shaft, or by the motor of the tool itself being driven in a pulsed manner. 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. Another desire in industrial assembly is rapid tightening operations since this may save time (and therefore costs) in the assembly procedure. This desire may typically contravene the requirement on high accuracy in installed torque. To speed up a tightening operation, high motor power must be used. However, high motor power may result in lower precision in installed torque. In conventional pulse tools, the same motor power (and thereby the same energy) is used for the pulses throughout the tightening operations. WO 2021151674 Al discloses a pulse tool allowing a user to set different power levels to be used during different stages of the tightening. Thus, the user can adjust the power level to be high in the beginning of a tightening up to a certain torque threshold, and then low as the torque exceeds that torque threshold, so that the tightening is performed with a lower power close to the target torque. Thus, the user is able to take the characteristics of the joint into consideration when setting the power for the pulses up to a certain torque threshold. It is possible to adapt the power so that the joint is tightened as fast as possible up to a certain torque threshold. It is also possible to achieve a more accurate tightening since the power can be set to a lower value close to the target torque. A shortcoming with this solution is that it requires manual input and knowledge of the characteristics of the joints that the strategy is to be applied to. Further, the pre-set power levels may not be optimal for all the joints to be tightened, in terms of speed and accuracy. Summary of the invention It would be advantageous to achieve a method and a control device overcoming, or at least alleviating, the above mentioned drawbacks. In particular, it would be desirable to provide a method and a control device that enable a better tailored trade-off between speed and accuracy of tightenings of different joints. To better address one or more of these concerns, a method and a control device having the features defined in the independent claims are provided. Preferable embodiments are defined in the dependent claims. Hence, according to an aspect, a method of controlling a motor of a pulse tool is provided. The pulse tool is arranged to provide torque in pulses during a tightening operation to tighten a threaded joint. The method comprises: - determining a parameter value indicative of a torque and/or angle increase achieved by a just performed pulse; - determining a motor power control parameter value for the next pulse based on said determined parameter value indicative of the torque and/or angle increase and such that said motor power control parameter value is kept between an upper limit and a lower limit; - controlling the motor according to the determined motor power control parameter value to create the next pulse; and repeating these steps until a target torque and/or angle is reached (and the tightening operation is ended). Further, the upper and lower limits are set so as to converge towards a predetermined final target window defining an allowable range within which the motor power control parameter value for the last pulse of the tightening operation is to be comprised. With the present aspect, the motor is controlled to output a power in the next (i.e. immediately succeeding) pulse dependent on the torque and/or angle increase achieved in the just performed (i.e. immediately preceding) pulse. Thereby, a control method is provided that will adjust the power (energy) of the motor during the tightening dependent on the characteristics of the joint. This enables a trade-off between speed and accuracy of the tightening that is tailored to the joint being tightened. For example, a soft joint will imply a lower increase in torque and higher increase in angle per pulse as compared to a hard joint. Due to the relatively small torque increase steps, softer joints may typically take longer time to tighten. The control method may detect this and determine a motor power control pa