Patent Application
20220105611
The present inventions relate to torque tools, and more particularly, to determining a torque applied by a power tool to a fastener.
Torque tools are commonly used in industrial settings to tighten fasteners to a specified torque. However, determining the actual torque applied by a power tool to a fastener can be difficult and inaccurate. Although determining the actual torque applied can be difficult for all power tools, impact wrenches are particularly difficult to accurately determine the actual torque applied to a faster. On the other hand, impact wrenches have several advantages over other torque tools, including a compact size, low tool weight and low cost. Thus, improved techniques for accurately determining the torque applied to a fastener would be desirable.
An improved power tool with torque control is described. The power tool estimates torque applied to a fastener by measuring the angle of rotation of the fastener and the energy expended by the tool to rotate the fastener through the angle of rotation. The power tool improves on the torque estimation by considering the efficiency of energy expended by the drive mechanism which may result in less energy (or more) being transferred to the fastener. The invention may also include any other aspect described below in the written description or in the attached drawings and any combinations thereof.
The invention may be more fully understood by reading the following description in conjunction with the drawings, in which:
Estimating the torque applied to a joint resulting from a fastening operation involving discrete blows may use measurements of the angular position of the joint and the change in angular position of the joint with each blow. This information may be coupled with knowledge of the energy in the impact mechanism before and after the blow. Ideally, if the energy leaving the tool in a given blow is measured, the mean torque multiplied by the change in joint angle will be equal to the energy output. Thus, if both the change in joint angle and the amount of energy leaving the tool during each blow are known, the joint torque can be estimated. That is, for a particular blow, the estimated mean joint torque can be determined from the energy that leaves the tool divided by the change in angular position of the threaded joint. It is noted, however, that other schemes involving assumptions about the joint's torque-versus-angle characteristic can also be used in conjunction with angle and energy measurements to estimate joint torque.
Angular position sensors may be placed on the anvil and on the hammer of an impact wrench to determine changes in angle rotation of the output shaft of the tool during a fastener tightening operation. This allows an approximation of the joint angular position and, via differentiating the hammer angular position, provides an estimate of the hammer angular velocity before and after an impact. The velocity change may then be used to determine the change in energy during an impact. That is, the velocity of the hammer will slow due to the impact force, which represents energy which is transferred from the hammer to the output shaft during the impact.
Various sensors may be used to improve torque estimates. A gyro is one type of sensor that may be used for the purpose of compensating for angular motion of the tool when computing angular rotation of the joint. A gyro may also be used to provide housing velocity information. A sudden change in the housing velocity following an impact indicates energy transfer from the mechanism to the housing. Preferably, this energy should be subtracted from that assumed to be utilized in tightening the joint. Various other sensors may also be used to improve estimates of joint torque based on tracking energy changes in addition to tracking the energy change of the impacting hammer. That is, additional and/or alternative sensors may be used to capture other energy that is lost and not transferred to the joint. For example, thermocouples may be used to measure the temperature of elements of the power tool, and thus, track changes in the thermal energy due to impact. This is particularly valuable for the impacting members themselves, but may also be extended to other parts of the tool as well. Accelerometer signals may also be integrated to determine the velocity of various components, allowing for the determination of energy associated with movement and vibration. Frequency analysis of accelerations may also be used in conjunction with peak values and analytical modal analysis to determine energies in vibratory modes excited by the impacts. Additional position sensors (e.g., angular and linear) may also be used to measure deformation and hence potential energy of tool components. Strain gauges may be used for a similar purpose. Other sensors that may be used include torque transducers, motor encoders/resolvers, and current and voltage probes. While the sensors mentioned above may be used for an improved torque estimation, it is understood that many other sensors may also be used to estimate energy changes. While the improved torque measurement methods herein are particularly useful with discrete energy tools like impact wrenches, it is understood that the energy tracking and angular measurement methods described herein may also be applied to continuous energy delivery tools.
Turning to
As shown in
T=E
H
/AR
where T is the estimated torque applied to the nut 28, EH is the change in energy of the hammer 16 (that is, drive mechanism 16) before and after an impact, and AR is the angular rotational movement of the nut 28 during the impact. The estimated torque may also be referred to as a residual torque, which is the torque value of the nut 28 or fastener after the power tool 10 has finished tightening the fastener (or at intermediate tightening steps). Preferably, the power tool 10 is provided with a preset torque setting, which may be user adjustable. In use, power to the motor 12 may be switched off when the estimated torque T applied to the nut 28 satisfies the preset torque setting to ensure proper tightening of the nut 28.
Although the above formula may be used as a basic estimate of torque applied to a fastener 28, the formula assumes perfect energy transfer from the drive mechanism 16 to the nut 28 and does not account for the efficiency of such energy transfer. Thus, an improved formula would adjust the energy value based on energy losses (or contributions) that change the actual energy transferred to the nut 28. Thus, the energy value in the above formula may be substituted with an actual energy as determined by the following formula:
E
Actual
=E
H
−E
V
−E
M
−E
T
−E
S
where EActual is an estimate of the actual energy transferred to the nut 28 which may be used in the formula above to determine the estimated applied torque, EH is the change in energy of the hammer 16 which may be the same value used in the basic formula above, EV is the energy of tool vibrations associated with an impact, EM is the energy of tool movements during the impact, ET is the energy of temperature changes during impact, and ES is the energy of tool sounds caused by the impact. It is also possible to recharacterize the above formula in terms of efficiency of torque transfer if desired (e.g., with other mathematical operators). For example, the loss in energy (or energy difference) can also be determined by multiplying the hammer energy EH by an efficiency factor. Sensor data from one or more sensors on the tool could be used to determine the efficiency factor for individual blows of the hammer as the tool is operated. For example, using prior testing of the tool, an efficiency correlation between data generated by the sensors and the efficiency factor can be formulated. The efficiency correlation may then be stored on the tool and applied to the sensor data that is generated during tool use to provide the efficiency factor, which can be varied as the tool is being used based on changing sensor data. It is understood that while tool vibrations and tool movements may be related to each other, tool vibrations have a frequency which are typically a multiple of the impact frequency, whereas tool movements may be other tool movements not considered to be vibrations.
Energy estimates may be made for each of the above energy values using a variety of sensors. Therefore, the energy formula above may be rewritten in terms of the sensors that may be used to estimate energy losses (or contributions) to be subtracted from the energy of the hammer 16. Thus, the rewritten formula may be:
E
Actual
=E
H
−E
A
−E
St
−E
G
−E
I
−E
VIt
−E
TT
−E
E
−E
Tc
−E
AP
where EActual and EH are described above, EA is the energy determined from an accelerometer, ESt is the energy determined from a strain gauge, EG is the energy determined from a gyro, EI is the energy determined from a current probe, EVIt is the energy determined from a voltage probe, ETT is the energy determined from a torque transducer, ETc is the energy determined from a thermocouple, and EAP is the energy determined from an air pressure sensor (e.g., a microphone).
It is understood that the above formulas may be modified as desired for a particular power tool. For example, it is possible to apply a factor to one or more energy values where it is determined that only a portion of the estimated energy associated with a condition or sensor is attributable to an energy loss (or contribution) transferred from the drive mechanism 16 to the output shaft 22. It is also possible that a smaller or greater number of conditions or sensors may be included in the actual energy estimate. Multiple sensors of the same type may also be used in various locations of the power tool 10 to improve the actual energy estimate. Further, multiple sensors may be used together to determine a particular energy estimate.
Examples of sensors that may be used to estimate energy losses (or contributions) are shown in
While preferred embodiments of the inventions have been described, it should be understood that the inventions are not so limited, and modifications may be made without departing from the inventions herein. While each embodiment described herein may refer only to certain features and may not specifically refer to every feature described with respect to other embodiments, it should be recognized that the features described herein are interchangeable unless described otherwise, even where no reference is made to a specific feature. It should also be understood that the advantages described above are not necessarily the only advantages of the inventions, and it is not necessarily expected that all of the described advantages will be achieved with every embodiment of the inventions. The scope of the inventions is defined by the appended claims, and all devices and methods that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.
