Torque control tool

Abstract

An electric power tool and a method of determining torque are provided. The method of determining torque estimates torque using energy output by a drive mechanism and a rotation angle of an output shaft. Energy is determined by subtracting efficiency loss (or gain) from a nominal energy of the drive mechanism, thereby improving torque estimation.

Description

Technical Field

[0001] This invention relates to torque tools, and more specifically, to determining the torque applied to a fastener by a power tool. Background Technology

[0002] Torque tools are commonly used in industrial environments to tighten fasteners to a specified torque. However, determining the actual torque applied to fasteners by power tools can be difficult and inaccurate. While determining the actual applied torque is difficult for all power tools, it is particularly challenging to accurately determine the actual torque applied to fasteners by impact wrenches. On the other hand, impact wrenches offer several advantages compared to other torque tools, including compact size, light weight, and low cost. Therefore, there is a need for improved techniques for accurately determining the torque applied to fasteners. Summary of the Invention

[0003] This invention describes an improved power tool with torque control. The power tool estimates the torque applied to the fastener by measuring the rotation angle of the fastener and the energy consumed by the tool to rotate the fastener by that rotation angle. The power tool improves torque estimation by taking into account the efficiency of the energy consumed by the drive mechanism (which may result in less (or more) energy being transferred to the fastener). The invention may also include any other aspects described in the following written description or drawings and any combination thereof. Attached Figure Description

[0004] The invention can be more fully understood by reading the following description in conjunction with the accompanying drawings, wherein:

[0005] Figure 1 This is a diagram of an impact wrench; and

[0006] Figure 2 It is a graph showing the relationship between rotation angle, torque, and energy. Detailed Implementation

[0007] The estimation of the torque applied to the joint resulting from a fastening operation involving discrete impacts can be achieved using measurements of the joint's angular position and its variation during each impact. This information can be combined with knowledge of the energy of the impact mechanism before and after the impact. Ideally, if the energy leaving the tool during a given impact is measured, the product of the average torque and the change in joint angle will equal the energy output. Therefore, if the change in joint angle and the energy leaving the tool during each impact are known, the joint torque can be estimated. That is, for a specific impact, the estimated average joint torque can be determined by dividing the energy leaving the tool by the change in the threaded joint's angular position. However, it should be noted that other assumptions regarding the joint torque-angle characteristics can also be used in conjunction with angle and energy measurements to estimate the joint torque.

[0008] An angular position sensor can be mounted on the anvil and hammer of an impact wrench to determine changes in the angular displacement of the tool's output shaft during a fastener tightening operation. This allows for the use of approximate values ​​of the joint's angular position and, by differentiating the hammer's angular position, provides an estimate of the hammer's angular velocity before and after impact. The velocity change can then be used to determine the change in energy during impact. That is, the hammer's velocity will decrease due to the impact force, indicating that energy is transferred from the hammer to the output shaft during impact.

[0009] Various sensors can be used to improve torque estimation. A gyroscope is a sensor that can be used to compensate for the angular motion of the tool when calculating the angular displacement of the joint. A gyroscope can also be used to provide housing velocity information. The sudden change in housing velocity after impact indicates that energy has been transferred from the mechanism to the housing. Preferably, this energy should be subtracted from the energy assumed to be used for tightening the joint. In addition to tracking the energy changes of the impact hammer, various other sensors can also be used to improve joint torque estimation based on the tracked energy changes. That is, additional and / or alternative sensors can be used to capture other energy that is lost and not transferred to the joint. For example, thermocouples can be used to measure the temperature of components of a power tool, thereby tracking changes in thermal energy caused by impact. This is particularly valuable for the impact component itself, but can also be extended to other parts of the tool. Accelerometer signals can also be integrated to determine the velocities of various components, thus allowing for the determination of the energy associated with motion and vibration. Frequency analysis of acceleration can also be combined with peak and analytical modal analysis to determine the energy in vibration modes excited by impact. Other position sensors (e.g., angular position sensors and linear position sensors) can also be used to measure the deformation of tool components and the resulting potential energy. Strain gauges can be used for similar purposes. Other sensors that can be used include torque sensors, motor encoders / resolvers, and current and voltage probes. While the aforementioned sensors can be used for improved torque estimation, it should be understood that many other sensors can also be used to estimate energy changes. Although the improved torque measurement method described in this paper is particularly useful for discrete energy tools such as impact wrenches, it should be understood that the energy tracking and angle measurement methods described in this paper can also be applied to continuously energy delivery tools.

[0010] Go to Figure 1 The figure shows a schematic diagram of power tool 10. While it is understood that the invention can be applied to other power tools, Figure 1 The schematic diagram relates to an impact wrench 10. Similar to conventional impact wrenches, the wrench 10 has a motor 12 that rotates a drive shaft 14, which in turn drives an impact drive mechanism 16. It should be understood that various types of motors and drive mechanisms can be used. However, in a preferred embodiment, the motor 12 is an electric motor 12, and the drive mechanism 16 is a hammer mechanism 16 with jaws 18 that engage and disengage with an anvil 20 on the proximal end of an output shaft 22. The power tool 10 also includes a tool housing 24 surrounding the motor 12 and the drive mechanism 16. A socket 26 may be disposed on the distal end of the output shaft 22 to engage a nut 28 of a threaded connector.

[0011] like Figure 2As shown, the torque applied to the nut 28 by the sleeve 26 can be determined by knowing the rotation angle of the output shaft 22 during a single impact of the drive mechanism 26 on the output shaft 22, and the energy transmitted from the drive mechanism 26 to the output shaft 22 within that rotation angle. Based on the known rotation angle and the transmitted energy, the torque applied to the nut 28 can be determined by the following formula:

[0012] T = E H / AR

[0013] Where T is the estimated torque applied to nut 28, and E H AR is the energy change of hammer 16 (i.e., drive mechanism 16) before and after the impact, and AR is the angular displacement of nut 28 during the impact. The estimated torque, also known as residual torque, is the torque value of nut 28 or fastener after the power tool 10 has completed tightening the fastener (or during an intermediate tightening step). Preferably, the power tool 10 is equipped with a preset torque setting that can be adjusted by the user. In use, when the estimated torque T applied to nut 28 meets the preset torque setting for ensuring proper tightening of nut 28, the power supply to motor 12 can be cut off.

[0014] While the above formula can be used as a basic estimate of the torque applied to fastener 28, it assumes perfect energy transfer from drive mechanism 16 to nut 28 and does not consider the efficiency of such energy transfer. Therefore, the improved formula adjusts the energy value based on changing the energy loss (or contribution) of the actual energy transferred to nut 28. Thus, the energy value in the above formula can be replaced by the actual energy determined by the following formula:

[0015] E Actual =E H –E V –E M –E T –E S

[0016] Among them, E Actual This is an estimate of the actual energy transmitted to nut 28, which can be used in the formula above to determine the estimated applied torque, E. H It is the energy change of hammer 16, which can be the same value used in the basic formula above, E V It is the energy of the tool vibration associated with the impact, E M It is the energy of the tool's movement during the impact, E T It is the energy of the temperature change during the impact, and E S This is the energy of the tool's sound caused by the impact. If necessary, the above formula can also be redefined based on the efficiency of torque transmission (e.g., using other mathematical operators). For example, energy loss (or energy difference) can also be expressed as the energy E of the hammer.H The efficiency factor is determined by multiplying the data by the efficiency factor. Sensor data from one or more sensors on the tool can be used to determine the efficiency factor of a single hammer strike when the tool is operated. For example, using prior testing of the tool, the efficiency correlation between the data generated by the sensors and the efficiency factor can be formulated. Furthermore, the efficiency correlation can be stored on the tool and applied to the sensor data generated during tool use to provide an efficiency factor that can vary based on the changing sensor data, depending on the tool being used. It should be understood that while tool vibration and tool motion can be correlated with each other, the frequency of tool vibration is typically a multiple of the impact frequency, while tool motion can be other tool motions that are not considered vibration.

[0017] Various sensors can be used to estimate the energy values ​​mentioned above. Therefore, the energy formula above can be rewritten based on sensors that can be used to estimate energy loss (or contribution), which will be subtracted from the energy of hammer 16. Thus, the rewritten formula could be:

[0018] E Actual =E H –E A –E St –E G –E I –E Vlt –E TT –E E –E Tc –E AP

[0019] Among them, E Actual and E H As mentioned above, E A The energy E is determined from the accelerometer. St The energy, E, is determined from the strain gauge. G The energy E is determined from the gyroscope. I The energy, E, is determined from the current probe. Vlt The energy, E, is determined from the voltage probe. TT The energy, E, is determined from the torque sensor. Tc The energy E is determined from the thermocouple. AP It is the energy determined from a barometric pressure sensor (such as a microphone).

[0020] It should be understood that the above formula can be modified according to the needs of a specific power tool. For example, a factor can be applied to one or more energy values, where it is determined that only a portion of the estimated energy associated with a state or sensor is attributable to energy loss (or contribution) transmitted from drive mechanism 16 to output shaft 22. It is also possible to include fewer or more states or sensors in the actual energy estimation. Multiple sensors of the same type can also be used at various locations on power tool 10 to improve the actual energy estimation. Furthermore, multiple sensors can be used together to determine a specific energy estimate.

[0021] Figure 1 The images show examples of sensors that can be used to estimate energy loss (or contribution). One type of sensor that can be used is an accelerometer 30, 32. Accelerometers 30, 32 can be located on the drive mechanism 16 and / or the tool housing 24. Accelerometers 30, 32 can be used to determine the vibrational or kinetic energy measured on the drive mechanism 16 and / or the tool housing 24. Another type of sensor that can be used is a strain gauge 34. Strain gauge 34 can be located on the tool housing 24 to determine the vibrational or kinetic energy measured on the tool housing 24. Another type of sensor that can be used is a gyroscope 36. Gyroscope 36 can be located on the tool housing 24 to determine the kinetic or vibrational energy measured on the tool housing 24. Another type of sensor that can be used is a current probe 38. Current probe 38 can be electrically connected to motor 12 to measure the current in motor 12, which can be used to determine the kinetic or vibrational energy. Another type of sensor that can be used is a voltage probe 40. Voltage probe 40 can be electrically connected to motor 12 to measure the voltage of motor 12, which can be used to determine kinetic or vibrational energy. It should be understood that current probe 38 and voltage probe 40 can also be used together to determine the power of motor 12, which can also be used to determine kinetic or vibrational energy. Another sensor that can be used is torque sensor 42. Torque sensor 42 can be located on motor 12 to measure the torque of motor 12 on drive shaft 14 or on the housing of motor 12, thereby determining kinetic or vibrational energy. Another sensor that can be used is encoders 44, 46, and 48. Encoders 44, 46, and 48 can be located near the distal end of output shaft 22, near the proximal end of output shaft 22, and / or on drive mechanism 16. Any angular position difference between encoders 44 can be used to determine kinetic or vibrational energy. It should be understood that encoders 44, 46, and 48 can also be used to determine the energy E of the hammer as described above. H(Especially the encoder 48 located on the drive mechanism) and the angular displacement AR as described above (especially one of the encoders 44 and 46 on the output shaft). Another sensor that can be used is a thermocouple 50. Thermocouple 50 can be located near the output shaft 22 (including near the output shaft bushing) to determine temperature energy. Another sensor that can be used is a barometric pressure sensor 52. Barometric pressure sensor 52 (e.g., microphone 52) can be located on the tool housing 24 to determine sound energy generated by the drive mechanism 16. It should be understood that, if desired, sensors can be used to determine more than one type of energy (e.g., vibrational energy and kinetic energy) or a single type of energy.

[0022] While preferred embodiments of the invention have been described, it should be understood that the invention is not limited thereto and modifications can be made without departing from the invention. Although each embodiment described herein may only mention certain features, and may not specifically mention every feature described for other embodiments, it should be recognized that the features described herein are interchangeable unless otherwise described, even if a particular feature is not mentioned. It should also be understood that the advantages described above are not necessarily the only advantages of the invention, and it is not necessarily expected that all the advantages described will be achieved through each embodiment of the invention. The scope of the invention is defined by the appended claims, and all apparatuses and methods within the meaning of the claims, whether literal or equivalent, are intended to be included in the claims.

Claims

1. A method for controlling a power tool, the method comprising: In response to the rotation of the output shaft by the drive mechanism, the rotation angle of the output shaft of the power tool is determined; Determine a first energy value for the power tool, wherein the first energy value is the energy change of the drive mechanism within the rotation angle; Determine a second energy value for the power tool, the second energy value being the energy of a component of the power tool within the rotation angle; as well as The residual torque of the fastener driven by the output shaft is determined based on the energy difference between the first energy value and the second energy value. The second energy value is the tool vibration energy, tool motion energy, tool temperature energy, or tool sound energy.

2. The method according to claim 1, further comprising turning off the electric motor used to drive the drive mechanism when the residual torque meets a preset torque setting.

3. The method according to claim 1, wherein, The first energy value is determined based on the speed difference between the drive mechanism before and after driving the output shaft through the rotation angle.

4. The method according to claim 1, wherein, The power tool in question is an impact wrench.

5. The method according to claim 1, wherein, The vibration energy of the tool is determined by an accelerometer, strain gauge, gyroscope, motor current probe, motor voltage probe, or torque sensor.

6. The method according to claim 5, wherein, The vibration energy of the tool is determined by the accelerometer, which is mounted on the drive mechanism used to drive the output shaft.

7. The method according to claim 5, wherein, The vibration energy of the tool is determined by the accelerometer, which is mounted on the tool housing surrounding the drive mechanism used to drive the output shaft.

8. The method according to claim 5, wherein, The vibration energy of the tool is determined by the strain gauge, which is mounted on the tool housing surrounding the drive mechanism used to drive the output shaft.

9. The method according to claim 5, wherein, The vibration energy of the tool is determined by the gyroscope, which is mounted on the tool housing surrounding the drive mechanism used to drive the output shaft.

10. The method according to claim 5, wherein, The vibration energy of the tool is determined by the motor current probe and / or the motor voltage probe, which respectively output the current and voltage of the electric motor for driving the drive mechanism, which is used to drive the output shaft.

11. The method according to claim 5, wherein, The vibration energy of the tool is determined by the torque sensor, which outputs torque to drive an electric motor of a drive mechanism, which in turn drives the output shaft.

12. The method according to claim 1, wherein, The motion energy of the tool is determined by an encoder, gyroscope, motor current probe, motor voltage probe, torque sensor, accelerometer, or strain gauge.

13. The method according to claim 12, wherein, The motion energy of the tool is determined by the encoder, which is mounted on the output shaft.

14. The method according to claim 12, wherein, The kinetic energy of the tool is determined by the gyroscope, which is mounted on the tool housing surrounding the drive mechanism used to drive the output shaft.

15. The method according to claim 12, wherein, The motion energy of the tool is determined by the motor current probe and / or the motor voltage probe, which respectively output the current and voltage of the electric motor for driving the drive mechanism, which is used to drive the output shaft.

16. The method according to claim 1, wherein, The temperature energy of the tool is determined by a thermocouple.

17. The method according to claim 16, wherein, The thermocouple is positioned adjacent to the output shaft.

18. The method according to claim 1, wherein, The sound energy of the tool is determined by a barometric pressure sensor.

19. The method according to claim 1, wherein, The energy difference between the first energy and the second energy is determined by multiplying the first energy value by an efficiency factor, wherein the efficiency factor is determined based on sensor data from one or more sensors on the power tool and the efficiency correlation between the sensor data stored on the tool and the efficiency factor.

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