TORQUE CONTROL DEVICE FOR PULSE TOOLS AND METHOD OF MONITORING TORQUE FOR PULSE TOOLS

Abstract

A non-intrusive torque control device for pulse tools, and a method of monitoring torque of pulse tools include steps of establishing a characteristic curve (FIG. 6) specify relation of revolution-per-minute (or BPM) with output torques for a specific pulse tool. Then establish another relationship curve (FIG. 7) specify operational factors (such as supply air pressure) with revolutions-per-minute (or BPM) for the same pulse tool at calibration stage. Those two curves and threshold are stored in flash memory of BPM detector (part of torque control system). The BPM detector is attached on the surface of pulse tool at nearby of impact mechanism. When fastening a bolt, at tightening stage while the impact reach the threshold stored in memory of BPM detector then start monitoring. This is a complete close loop torque control exclusive for pulse tool only. Target torque can be pre-set manually or automatically if a wireless control proportional valve is available connected to air source. In other word, impact mechanism inside pulse tool is same as install single or double hammer Increase BPM (rpm) of impact mechanism has the same effect as increase hammer knocked speed and has been proven by characteristic curve (FIG. 6).

Claims

1. A method of monitoring torque for pulse tools, comprising: connecting a pulse tool to a power source, a torque controller, and a beat-per-minute detector (BPM detector), wherein a torque measurement platform is used for pulse tool at tightening process to perform calibration procedure, where the threshold of output torque is stored in a flash memory of the BPM detector; calibrating the relationship of revolution-per-minute (or BPM) with output torques of the pulse tool, then establishing a characteristic curve and stored in memory of the BPM detector and the torque controller; calibrating the relationship of operation factors with revolution-per-minute (or BPM) of pulse tool, then establishing a relation curve and stored in memory of the BPM detector and the torque controller.

2. The method as claimed in claim 1, further comprising: connecting the BPM detector to the pulse tool while pulse tool is operated, the torque measurement platform defining the threshold and stored in the storage unit of the BPM detector; and through the torque measurement platform establishing a characteristic curve specify relationship of revolutions-per-minute (or BPM) with the output torques and a relationship curve specify relationship of operation factor with revolutions-per-minute (or BPM) for a specific pulse tool at tightening process, then stored in the memory unit of the torque controller.

3. The method as claimed in claim 1, further comprising using a microprocessor in the torque controller to compare BPM values with a preset value of the BPM detector at tightening process within tolerance range, a warning signal generated when the values detected by the BPM detector fall outside a tolerance range.

4. The method as claimed in claim 1, wherein a pulse tool which has been calibrated before runs through a confirmation on the torque measurement platform, the confirmation including comparing BPM values detected from the BPM detector and output torque of the pulse tool to be matched with the characteristic and relation curves of a specific pulse tool.

5. The method as claimed in claim 2, wherein a pulse tool which has been calibrated before runs through a confirmation on the torque measurement platform, the confirmation including comparing BPM values detected from the BPM detector and output torque of the pulse tool to be matched with the characteristic and relation curves of a specific pulse tool.

6. The method as claimed in claim 3, wherein a pulse tool which has been calibrated before runs through a confirmation on the torque measurement platform, the confirmation including comparing BPM values detected from the BPM detector and output torque of the pulse tool to be matched with the characteristic and relation curves of a specific pulse tool.

7. A torque control device for pulse tools, comprising: a proportional valve connected between a pulse tool and a pressurized air source, the proportional valve receiving operational conditions of torque-setting from a torque controller, and adjustable operational factors by setting operational parameters; a beat-per-minute detector (BPM detector) attached on surface of pulse tool with accelerometer as core component to detect pulses generated by pulse tool at tightening process to calculate BPM, then compute BPM into revolutions per minute depends on single or double hammer mechanism inside pulse tool; a torque controller with a micro processer, a characteristic curve of BPM related with output torque and an operation curve of BPM or RPM relate with operation parameters such as pressure of supply air source of specific pulse tool was set up at calibration stage; and a storage unit located in the BPM detector and storing threshold of pulse tool, characteristic curve and relationship curve wherein, before a fastening process, the torque controller converts target torque set by user into revolutions-per-minute or BPM, and operation parameter corresponding to target torque referred from characteristic curve and operation curve stored in flash memory at calibration stage, and wherein, during a fastening process, the torque controller compares BPM values from the BPM detector with BPM corresponds to target torque specified at characteristic curve stored in the microprocessor to judge whether the output torques from the pulse tool fall within a tolerance range of target values or not, if not then show a warning signal, to thereby match a close loop control.

8. The torque control device of claim 7, wherein the BPM detector, torque calibration platform, and proportional valve are in communication with each other through wireless communication.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 shows that a BPM detector is attached to surface of pulse tool at a nearby impact mechanism;

[0026] FIG. 2 shows that the BPM detector is removed from the pulse tool;

[0027] FIG. 3 is an exploded view to show the BPM detector of the present invention;

[0028] FIG. 4 shows that the pulse tool is connected to the BPM detector and the proportional valve to check the output torque;

[0029] FIG. 5 shows the operation of the present invention;

[0030] FIG. 6 shows the characteristic curve specify relationship of revolution-per-minute (or BPM) and output torque of specific pulse tool for present invention.

[0031] FIG. 7 shows the relationship curve specify operational factors (such as supply air pressure) and revolutions-per-minute (or BPM) for the same pulse tool of present invention.

[0032] FIG. 8 shows the Evaluation data of present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0033] Referring to FIGS. 1 to 8, the non-intrusive method of monitoring torque of pulse tools comprises the following steps:

[0034] A step of connecting a pulse tool 1 to a stable power source such as a pressurized air source or an electric power source, a proportional valve 5, a torque controller 3, and a beat-per-minute detector 2 (BPM detector) which can also be integral with the torque controller 3. At tightening process, the pulse tool 1 is connected with a torque measurement platform 4 to detect an output torque from the pulse tool 1 so as to obtain torque and threshold stored in a storage unit in the BPM detector 2. When a value detected is below the threshold, this means that the pulse tool 1 is at free spin status (not at tightening process).

[0035] A step of establishing a characteristic curve specified relationship of revolution-per-minute (or BPM) and output torque of specific pulse tool 1. The characteristic curve is obtained when the pulse tool 1 is at tightening process. The characteristic curve is stored in a memory unit of the torque controller 3.

[0036] A step of establishing a relationship curve specified operational factors (such as supply air pressure) and revolutions-per-minute (or BPM) for the same pulse tool 1. The relationship curve is stored in the memory unit of the torque controller 3.

[0037] When fastening a bolt, the target torque is set by user into torque controller 3, and user refers related BPM and operation factors (such as air pressure) displayed on controller calculated from the characteristic curve and the relationship curve. Real operation factors such as air pressure can be set by user manually or set by wireless proportional valve 5 automatically if available. At tightening process the BPM detector 2 keeps monitoring whether or not the output torque from the pulse tool 1 falls in the tolerance range of the target torque so as to achieve the purpose of monitoring the output torque.

[0038] The output torque from the pulse tool 1 is:

[00003]$\begin{array}{cc}T=rF=rma=rm\frac{d.Math.V}{d.Math.t}& \left(\mathrm{formula}.Math..Math.1\right)\end{array}$

[0039] The maximum tangent speed of impact unit is:

[00004]$\begin{array}{cc}\mathrm{Vt}=2.Math.P.Math.i\frac{r}{d.Math.t}=r\frac{2.Math.P.Math.i}{d.Math.t}=r& \left(\mathrm{formula}.Math..Math.2\right)\end{array}$

[0040] The initial tangent speed of impact unit at tightening process at each cycle start is:

Vi=0 (formula 3)

[0041] The speed difference of the impact unit (the radius of the impact unitangular speed):

[00005]$\begin{array}{cc}\mathrm{dV}=\mathrm{Vt}-\mathrm{Vi}=2.Math.P.Math.i\frac{r}{d.Math.t}=r\left(\frac{2.Math.P.Math.i}{d.Math.t}\right)=r& \left(\mathrm{formula}.Math..Math.4\right)\end{array}$

[0042] The speed difference dv is applied into the formula 1:

[00006]$\begin{array}{cc}T=rm\frac{d.Math.V}{d.Math.t}=rmr\frac{}{d.Math.t}=m\left(\frac{r^2}{d.Math.t}\right)=IC=J& \left(\mathrm{formula}.Math..Math.5\right)\end{array}$

[0043] The output torque of the pulse tool 1 at tightening process is decided by the maximum angular speed . The average angular speed of each impact is reasonably deemed as . The rotational speed of the impact unit is

[00007]$\mathrm{rpm}=\left(\frac{2.Math.P.Math.I}{6.Math.0}\right).Math.\frac{\mathrm{radian}}{s}=\left(\frac{2.Math.P.Math.I}{6.Math.0}\right)\left(\frac{1}{2}.Math.\right)=\left(\frac{P.Math.i}{6.Math.0}\right)$

[0044] It is difficult to detect the maximum angular speed and the impact time dt. However, there are many ways to detect the rotational speed of the impact unit rpm, including adding an encoder at rear end of the motor, but it is not feasible as mention above.

[0045] It is suggested to attach a BPM detector on surface of pulse tool 1 at nearby of impact mechanism, and the threshold is set so as to detect BPM as rpm (single hammer mechanism) or rpm (double hammer mechanism).

[0046] The dt means the period of time at tightening process, when the tangent speed drops from the maximum tangent speed to 0 of the impact unit at end of each impact cycle. The dt may vary along with different material of the impact unit, and the difference of the dt is deemed as a constant C because material of impact mechanism is steel most likely. The rotational momentum is I=m(r.sup.2) which is applied into the formula 5 so that the output torque of the pulse tool 1T=IC=J.

[0047] The output torque T is proportion to the rotational speed of the impact unit, and can be related from the characteristic curve. The rotational speed or angular speed of the pulse tool 1 at tightening process is directly proportional to the output torque T of the impact unit within a certain range.

[0048] Under different operational conditions such as pressure, air flow, conditions of the motor, rpm of the pulse tool 1 at tightening process is affected as shown at relationship curve. By checking relationship curve, rpm of the impact unit at tightening process can be monitored so as to control the output torque through referring characteristic curve to achieve purpose of torque control.

[0049] The present invention may refer one of specific operational factors (pressure, flow, or impact mechanism) as operational factor to build the relation curve with rpm of pulse tool 1. At tightening process, angular speed raises from 0 at cycle start to the maximum angular speed .

[00008]$\mathrm{The}.Math..Math.\mathrm{maximum}.Math..Math.\mathrm{tangent}.Math..Math.\mathrm{speed}.Math..Math.\mathrm{Vt}=2.Math.\mathrm{Pi}r..Math.\mathrm{Speed}.Math..Math.\mathrm{difference}.Math..Math..Math..Math.V=\mathrm{Vt}-V.Math.i=2.Math.P.Math.ir$$\mathrm{Impact}.Math..Math.\mathrm{momentum}.Math..Math.\mathrm{momentum}=m.Math..Math.V$$\mathrm{Impact}.Math..Math.\mathrm{force}.Math..Math.F=m\frac{.Math.V}{.Math.t}..Math.\mathrm{Pulse}.Math..Math.\mathrm{torque}.Math..Math.T=rF=r^{2}2.Math.P.Math.i=IC=J.$

[0050] Output torque T of the pulse tool 1, at tightening process is directly proportional to BPM (angular speed ) as seen in the characteristic curve 6 of specific pulse tool.

[0051] Power=Air pressureAir flow drives air motor to rotate impact unit 1, the maximum angular speed can be controlled by the control of the operational factors as stated in relation curve 7.

[0052] If pulse tool 1 isn't at tightening process, for instance free spin, the output shaft of the pulse tool is co-rotated with the impact unit. Tangent speed Vt=2Pir does not drop to 0. In other words, both angular rate and tangent speed V keep constant, except speed difference V=0. Even though the total dynamic energy is built up at output shaft of pulse tool 1, still zero output torque is presented at pulse tool 1 due to zero momentum (V=0). This is a key reason to explain why BPM detector is suitable for torque control of pulse tool other than encoder attached at end of motor. Encoder is capable of detecting angular speed but has no way to judge whether or not pulse tool is at tightening process.

[0053] As shown in FIGS. 1 to 5, the BPM detector 2 is connected to the surface of pulse tool 1. Place pulse tool 1 on measurement platform 4 to start calibration. At tightening process, threshold obtained from the torque measurement platform 4 is stored in the storage unit of the BPM detector 2. Relationship between BPM and output torque to establish characteristic curve, and relationship between BPM and operation factors (such as supply air pressure) to establish relationship curve are stored in memory as well.

[0054] As shown in FIGS. 1 to 5, the torque control device for pulse tools of the present invention is connected between the power source and the pulse tool 1, and comprises a BPM detector 2 which uses the accelerometer 21 to detect the beats per minute of the impact unit, and the beats per minute of the impact unit is used to calculate the revolutions per minute. A torque controller 3 has a micro processer so as to establish a characteristic curve between revolution-per-minute of an impact unit in the pulse tool 1 and output torques of the pulse tool 1, and a relationship curve between operational factors of the pulse tool 1 and the revolutions-per-minute of the impact unit in the pulse tool 1. The two curves are stored in the microprocessor of the torque controller 3. When set target torque in pulse tool 1, the target value is input to the torque controller 3, and the torque controller 3 calculates the revolutions per minute of the impact unit corresponding to the target value. The operational factors are displayed on the liquid display panel of the torque controller 3. If there is a proportional valve 5, the proportional valve 5 automatically adjusts the operational factors corresponding to the target torque. Otherwise, the operational factors can be adjusted manually according to the display information on the display panel. When pulse tool 1 start to fasten a bolt, BPM Detector checks the characteristic curve and the relationship curve at tightening process. The microprocessor in torque controller 3 compares the BPM values and checks whether or not the BPM values fall into the tolerance range. If the BPM values fall into the tolerance range, a green LED lights up, if the BPM values fall out of the tolerance range, a warning red LED lights up.