Title: Processes of determining torque output and controlling power impact tools using a torque transducer
Abstract: An impact tool having a control system for turning off a motor at a preselected torque level.
Patent Number: 6,892,826 Issued on 05/17/2005 to Giardino
| Inventors:
|
Giardino; David A. (Rock Hill, SC)
|
| Assignee:
|
Chicago Pneumatic Tool Company (Rock Hill, SC)
|
| Appl. No.:
|
338622 |
| Filed:
|
January 7, 2003 |
| Current U.S. Class: |
173/1; 73/862.23; 173/176; 173/181; 173/183 |
| Intern'l Class: |
B25D 023/14 |
| Field of Search: |
173/1,176,178,180,181,182,183,2
81/467,470
73/862.23,862.24,761
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Smith; Scott A.
Attorney, Agent or Firm: Schmeiser, Olsen & Watts
Parent Case Text
This application is a divisional of Ser. No. 09/872,121, filed on Jun. 1, 2001
now U.S. Pat. No. 6,581,696, which is a continuation-in-part of Ser. No. 09/204,698,
filed on Dec. 3, 1998 now U.S. Pat. No. 6,311,786.
Claims
1. An method comprising:
providing a sensor measuring a time varying force signal of a plurality of impacts;
calculating a torque from said time varying force signal;
providing a control system for receiving a torque data signal from the sensor;
and
wherein the control system turns off a motor at a preselected torque level.
2. The method of claim 1, wherein the sensor provides the torque data signal
from an output shaft driven by an impact transmission mechanism driven by the motor.
3. The method of claim 1, further including providing an input device for inputting
the preselected torque level to the control system.
4. The method of claim 3, wherein the input device is a keypad.
5. The method of claim 1, further including the step of providing an output device
connected to the control system for providing output data from the control system.
6. The method of claim 5, wherein the output device is a liquid crystal display.
7. The method of claim 1, further including the step of providing a power supply
to supply power to the control system.
8. The method of claim 7, wherein the power supply is chosen from the group consisting
of a battery, a solar cell, a fuel cell, an electrical wall socket and a generator.
9. The method of claim 1, wherein the control system further includes a switch
to turn on or off the motor.
10. The method of claim 9, wherein the switch comprises an electrical switch
to turn on or off an electrical current to the motor.
11. The method of claim 9, wherein the switch comprises a shut off valve for
turning on or off a gas supply to the motor.
12. The method of claim 9, further including an activation trigger for turning
on the motor.
13. The method of claim 1, wherein the motor comprises a pneumatic motor.
14. The method of claim 1, wherein the motor is an electric motor.
Description
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to processes for determining torque output and
controlling power impact tools. The invention also relates to a mechanical impact
wrench having electronic control.
2. Related Art
In the related art, control of power impact tools has been accomplished by directly
monitoring the torque of impacts of the tool. For instance, in U.S. Pat. Nos. 5,366,026
and 5,715,894 to Maruyama et al., incorporated herein by reference, controlled
impact tightening apparatuses are disclosed in which complex processes involving
direct torque measurement are used. Direct torque measurement involves the measurement
of the force component of torsional stress, as exhibited by a magnetic field about
a tool output shaft, at the point in time of impact. From this force component,
related art devices directly determine the torque applied during the impact, i.e.,
torque T=force F times length of torque arm r. As exemplified by FIG. 10 of U.S.
Pat. No. 5,366,026, however, torque measurements fluctuate, even after a large
number of impacts are applied. This phenomena is caused by the inconsistent nature
of the force component of the impact. In particular, some devices measure torque
at a given point in time, such that the torque measured is based on whatever force
is being applied at that point in time. In other cases, the force is monitored
as it rises, and is measured for peak at a point in time at which a force decrease
is detected. In either case outlined above, the force may not be the peak force
and, hence, the peak torque derived may not be accurate.
To rectify this problem, related art devices use weighting factors, or peak and/or
low pass filtering of torque peak measurement, and/or assume, even though it is
not the case, a constant driving force from the motor. For instance, in U.S. Pat.
No. 5,366,026, torque measurements are used to calculate a clamping force based
on the peak value of a pulsatory torque and an increasing coefficient that represents
an increasing rate of a clamping force applied. Unfortunately, torque measurement
accuracy remains diminished. Accordingly, there exists a need for better processes
of operating power impact tools and, in particular mechanical impact tools (i.e.,
those with mechanical impact transmission mechanisms), with greater accuracy of
torque measurement. There also exists a need for more accurate torque measurement.
Another shortcoming of the related art is the lack of an electronic control
in a mechanical impact wrench.
SUMMARY OF THE INVENTION
The present invention provides an impact tool having a control system for turning
off a motor at a preselected level.
The present invention provides a mechanical impact wrench comprising:
- a housing;
- an impact transmission mechanism within the housing;
- an output shaft driven by the impact transmission mechanism;
- a motor to power the transmission mechanism;
- a ferromagnetic sensor measuring an output torque of the output shaft; and
- a control system for receiving a torque data signal from the ferromagnetic
sensor, wherein the control system turns the motor off at a preselected torque level.
The present invention provides a method comprising:
- providing a control system for receiving a torque data signal from a
ferromagnetic sensor; and
- wherein the control system turns off a motor at a preselected torque level.
The foregoing and other features and advantages of the invention will be apparent
from the following more particular description of preferred embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The preferred embodiments of this invention will be described in detail, with
reference to the following figures, wherein like designations denote like elements,
and wherein:
FIG. 1 shows a power tool in accordance with the present invention;
FIGS. 2A-2C show a flowchart of the processes in accordance with the present invention;
FIG. 3 shows another embodiment of a power tool including a ferromagnetic sensor
for measuring an output torque of an output shaft and a control system for turning
the motor off at a preselected torque level;
FIG. 4 shows another embodiment of a power tool including an input device for
inputting the preselected torque level located external from the housing; and
FIG. 5 shows a schematic view of the control system for turning off the power
tool when a preselected torque level is reached.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Although certain preferred embodiments of the present invention will be
shown and described in detail, it should be understood that various changes and
modifications may be made without departing from the scope of the appended claims.
The scope of the present invention will in no way be limited to the number of constituting
components, the materials thereof, the. shapes thereof, the relative arrangement
thereof, etc., which are disclosed simply as an example of the preferred embodiment.
Referring to FIG. 1, a power impact tool
10 in accordance with the
present invention is shown. It should be recognized that while power impact tool
10 is exemplified in the form of a mechanical impact wrench, the teachings
of the present invention have applicability to a diverse range of power impact
tools. Hence, although the teachings of the present invention provide particular
advantages to a mechanical impact wrench, the scope of the invention should not
be limited to such devices.
The power tool
10 includes a housing
11 for a motor
12 (shown
in phantom), e.g., electric, pneumatic, hydraulic, etc. Housing
11 includes
a handle
14 with activation trigger
16 therein. Power tool
10
also includes a mechanical impact transmission mechanism
21 having an output
shaft or anvil
18, and a hammer
22, possibly coupled to output shaft
or anvil
18 by an intermediate anvil
24. Hammer
22 is rotated
by motor
12 via motor output
20 to physically and repetitively strike
or impact output shaft or anvil
18 and, hence, repetitively transmit an
impact through socket
38 to workpiece
40. It should be recognized
that impact transmission mechanism
21 may take a variety of other forms
that are recognized in the art and not diverge from the scope of this invention.
Further, it should be recognized that socket
38 may take the form of any
adapter capable of mating with workpiece
40 to output shaft
18, and
that the workpiece
40 could also be varied. For instance, the workpiece
could be a nut, bolt, etc.
Power tool
10 additionally includes a shutoff
15 located preferably
in the handle
14. The shutoff
15, however, could be located in housing
12, or pressurized fluid supply line
17 if one is required. The pressurized
fluid supply line
17 may carry any suitable substance (e.g., gas, liquid,
hydraulic fluid, etc.) Shutoff
15 is activated by data processing unit or
electronic control
50 to stop operation of power tool
10, as will
be described below. While electronic control
50 is shown exterior to power
tool
10, it may also be provided within power tool
10, if desired.
If power tool
10 is a pneumatic tool, shutoff
15 is a shutoff valve.
If an electric motor is used, shutoff
15 can be embodied in the form of
a control switch or like structure.
Power tool
10, in the form of a mechanical impact wrench, includes a
ferromagnetic sensor
30. Sensor
30 is permanently attached as shown,
however, it is contemplated that the device can be replaceable for ease of repair.
Sensor
30 includes a coupling
32 for connection to a data processing
unit
50, a stationary Hall effect or similar magnetic field sensing unit
34, and a ferromagnetic part
36. Preferably, the ferromagnetic part
36 is a magneto-elastic ring
37 coupled to the output shaft
18
of power tool
10. Such magneto-elastic rings
37 are available from
sources such as Magna-lastic Devices, Inc., Carthage, Ill. In the preferred embodiment,
the magneto-elastic ring
37 surrounds or is around the output shaft
18.
The use of a separate ferromagnetic element
36, when replaceable, allows
easy and complete sensor replacement without changing output shaft
18 of
mechanical impact wrench
10, therefore, reducing costs. Further, the preferable
use of a magneto-elastic ring
37 increases the longevity of mechanical impact
tool
10 because ring
37 can withstand much larger impacts over a
longer duration. It should be noted, however, that the above-presented teachings
of the invention relative to the sensor are not intended to be limiting to the
invention's other teachings. In other words, the embodiments of the invention described
hereafter do not rely on the above-described sensor for their achievements.
Turning to the operation of power tool
10, an important feature of
the invention is that sensor
30 is used to measure a time varying force
signal or, in other words, the impulse of the impacts. This determination of impulse
is then used to calculate torque as opposed to measuring it directly. Directly
measuring torque, as in the related art, leads to inaccurate indications because
of the point in time aspect of the measurement, hence, requiring the use of correction
factors, peak and/or low pass filtering of torque peak measurements, or inaccurate
assumptions of constant torque output. In contrast, including a time parameter
which can be integrated allows for a more accurate perspective of tool activity.
Since impulse is directly related to torque, the torque values corresponding to
the determined impulse values can be derived to obtain more accurate torque values.
Impulse I is generally defined as the product of force F and time t. As used
in the present invention, impulse I is equationally represented as:
##EQU1##
Where F is the force of the impact, dt is the differential of integration of
time from t
i, the time of integration initiation, to t
f,
the time of integration conclusion. Impulse, as used herein, is the integration
of the product force and time over a desired time duration. It should be recognized
that there are a variety of ways of setting t
i and t
f. For
instance, in the preferred embodiment, data is continuously streamed into a buffer
in data processing unit or electronic control
50. When an impact is detected,
t
i is set to be impact minus some number (x) of clock counts, and t
f
is set to be impact plus some number (y) of clock counts. The parameters
(x) and (y) are dependent on the tool used. As a result, a window of the force
is created from t
i to t
f which can be integrated to derive
an impulse value.
Torque is preferably derived from the determination of impulse as follows.
Impulse I is also equivalent to change in linear momentum Δρ, i.e.,
I=Δρ. Linear momentum ρ can be converted to angular momentum
L by taking the vector product of the impulse I and length of a torque arm r, i.e.,
L=r×ρ. Torque T, while generally defined as force times length of torque
arm r, can also be defined in terms of the time rate of change of angular momentum
on a rigid body, i.e., ΣT=dL/dt. Accordingly, impulse I can be converted
to torque T using the following derivation:
Therefore, the torque acting over the time duration t of the impact is
T=Ir/t. Knowing the impulse I, the torque arm r, and the time duration t, an accurate
measure of torque T can be derived from a determination of the impulse. The impulse
value I can also be multiplied by a coefficient of proportionality C prior to determination
of the torque T. The coefficient of proportionality C is a predetermined value
based on the size of the particular tool, e.g., it may vary based on area of magnetic
field and manufacturing tolerance.
FIGS. 2A-2C show a flowchart diagram of process embodiments of the present
invention. In step S
1, the user of the power tool
10 inputs selected
parameter standards, or targets, for the given workpiece
40. "Standards"
refers to individual target values, i.e., maximum allowable torque T
max,
minimum number of impacts N
min, etc., or desired target value ranges,
i.e., T
min<T<T
max, N
min<N<N
max,
or t
min<t<t
max, etc. While in the preferred embodiment,
torque T is the main parameter for tool control and two cross-checking parameters
(i.e., impact number N and time duration t) are used, it should be recognized that
other parameters can be measured and used for cross checking proper operation on
a given workpiece.
Next, in step S
2, the system is queried for: operational inputs, e.g.,
standards outlined above; outputs/reports to be generated and/or printed; data
to be stored and/or reviewable; and whether the user is ready to use the tool.
A ready light may be used to indicate the tool readiness for operation or to receive
data. If the ready indication is not triggered, the process loops until a ready
indication is given. When a ready indication is given, the process progresses to
step S
3 where the parameters to be measured are initialized, i.e., values
of torque T
o, and impact time duration t
o are set to 0, and
the number of impacts N is set to 1.
At step S
4, the in-operation process loop of power tool
10 begins.
Monitoring of sensor
30 output is constant except when the standards are
met or an error indication is created, as will be described below. The in-operation
process loop begins when the monitoring of sensor
30 indicates operation
of the tool by sensing an impact. Because an impact threshold occurs sometime after
the start of an impact, a window of the data (which is collected in a buffer of
electronic control
50) from the monitoring of sensor
30 that spans
the impact threshold is used. As discussed above, when an impact is detected, t
i
is set to be impact minus some number of clock counts. Accordingly, when an initial
impact is sensed, the system can go back (x) clock counts to determine where the
in-operation processing should begin. If no operation is sensed, the process loops
until operation is sensed.
When operation is activated, the process proceeds to step S
5 where data
collection is made. In the preferred embodiment, impulse I, number of impacts N,
and time duration t are measured. Impulse I is created by integrating over time
the force applied as described above. Torque T is then calculated or derived from
impulse I according to the above described derivation at step S
6.
Next, as shown in FIG. 2A, at step S
7, and FIG. 2B S
8-S
12,
the data collected is compared to inputted standards, or a combination thereof.
Specifically, at step S
9, a determination of whether t>t
max
is made; at step S
10, a determination of whether N>N
max is
made; and at step S
11, a determination of whether T>T
max is
made. Combinations of standard checking can be advantageous also. For example,
at step S
8, determinations of whether t<t
min and T>T
min
are made; and at step S
12, determinations of whether N<N
min
and T>T
min are made. Other comparisons are also possible.
As indicated at step S
13, when the standards are not met, a red error
light
is turned on. Simultaneously, electronic control
50 activates shutoff
15
and operation stops. At step S
14, an appropriate error signal is created
depending on which parameter is violated, e.g., T
oerr, N
oerr,
t
oerr, T
uerr, N
uerr, t
uerr, etc. The
subscript "oerr" symbolizes that a maximum value, e.g., T
max, was exceeded,
and the subscript "uerr" symbolizes that a minimum value, e.g., N
min,
was not met. Error statements that do not indicate whether the error is based on
high or low violation also could be used, e.g., t
err. At step S
15,
any necessary target resets are produced. At step S
16, the red light is
turned off and the process then returns to step S
2 to begin operation again,
if desired.
Preferably, control of power tool
10 is based on torque T, as
derived from impulse I, alone. As mentioned above, however, the use of multiple
standards and multiple standard checking allows for a cross-checking for proper
operation on a given workpiece. A possible inappropriate outcome on, for example,
a bolt and nut workpiece is where the bolt and nut are cross threaded. In this
example, where torque measurements indicate a proper connection, number of impacts
N may not meet standards, thus indicating the presence of cross threading.
If no error is indicated at steps S
7-S
12, operation of the tool
loops back to step S
4. During the loop, at step S
17, the number of
impacts N is incremented by one.
Through steps S
7-S
12, the system also determines when the standards
are satisfactorily met. That is, when T
min<T<T
max;
N
min<N<N
max; and t
min<t<t
max,
etc., are satisfied. When this occurs, the process proceeds to step S
18,
as shown in FIG.
2C. At step S
18, a green light is turned on indicating
proper operation on the workpiece, and simultaneously tool operation is stopped
by electronic control
50 activating shutoff
15.
At step S
19, statistical analysis of the operation is conducted. For instance,
the final number of impacts N, the average torque T applied, the range R of torque
T applied, or standard deviation S can be calculated. It should be noted that other
processing of data can occur and not depart from the scope of the invention. For
example, statistical values such as: mean average, ranges, and standard deviations,
etc., of all measured parameters can be calculated, if desired. Further, error
indicators can also be created based on these statistical values, if desired.
At step S
20, the data gathered and/or calculated is displayed and/or written
to data storage, as desired.
At step S
21, the process waits X(s) amount of time before turning off
the
green light and proceeding to step S
2 for further operation as desired by
the user. The process then returns to step S
2 to begin operation again.
The above process of measuring impulse and deriving torque values therefrom provides
a more accurate control of power tool
10.
FIG. 3 shows another embodiment of a power tool
10A. The power tool
10A
includes a housing
11 for a motor
12 (shown in phantom). The motor
12 may comprise any suitable drive means (e.g., electric, pneumatic, hydraulic,
etc.). The housing
11 includes the handle
14 with the activation
trigger
16 therein. The power tool
10A also includes the mechanical
impact transmission mechanism
21 having the output shaft or anvil
18,
and the hammer
22, selectively coupled to the output shaft or anvil
18
by the intermediate anvil
24. Hammer
22 is rotated by the motor
12
via the motor output
20 to physically and repetitively strike or impact
the output shaft or anvil
18 and, hence, repetitively transmit an impact
through socket
38 to the workpiece
40. It should be recognized that
impact transmission mechanism
21 may take a variety of other forms that
are recognized in the art and not diverge from the scope of this invention. Further,
it should be recognized that socket
38 may take the form of any adapter
capable of mating workpiece
40 to output shaft
18, and that the workpiece
40 could also be varied. For instance, the workpiece
40 could be
a nut, bolt, etc.
The power tool
10A includes a switch
15A located in the handle
14. The switch
15A, however, could be located in the housing
12,
or pressurized fluid supply line
17 if one is required. The switch
15A
is included in a control system
50A. The switch
15A is activated
by the control system
50A to stop operation of the power tool
10A.
The control system
50A may be located within the power tool
10A,
or may be exterior to the power tool
10A. If the power tool
10A is
a pneumatic tool, the switch
15A is a shutoff valve. If an electric motor
is used, the switch
15A may comprise an electrical control switch.
The power tool
10A, in the form of a mechanical impact wrench includes
a torque transducer such as the ferromagnetic sensor
30. The ferromagnetic
sensor
30 is permanently attached as shown, however, the ferromagnetic sensor
30 may be replaceable for ease of repair. Ferromagnetic sensor
30
includes the coupling
32 for connection to the control system
50A,
a stationary Hall effect or similar magnetic field sensing unit
34, and
a ferromagnetic part
36. The ferromagnetic part
36 may be a magneto-elastic
ring
37 coupled to the output shaft
18 of the power tool
10A.
Such magneto-elastic rings
37 are available from sources such as Magna-lastic
Devices, Inc., Carthage, Ill. The magneto-elastic ring
37 may surround or
is around the output shaft
18.
The use of a separate ferromagnetic element
36, when replaceable, allows
easy and complete sensor replacement without changing output shaft
18 of
the mechanical impact wrench
10A, therefore, reducing costs. Further, the
preferable use of the magneto-elastic ring
37 increases the longevity of
mechanical impact tool
10A because ring
37 can withstand much larger
impacts over a longer duration.
In the power tool
10A, the ferromagnetic sensor
30 measures an
output
torque level
84 in the output shaft
18. A conduit
60 carries
a torque data signal
62 including the output torque level
84 to the
control system
50A. A conduit
64 carries input data
66 from
an input device
68 to the control system
50A. A conduit
70
carries output data
72 to an output device
74. A conduit
76
carries power
78 from a power supply
80 to the control system
50A.
The power supply
80 may be any suitable source (e.g., a battery, a solar
cell, a fuel cell, an electrical wall socket, a generator, etc.). The input device
68 may be any suitable device (e.g., touch screen, keypad, etc.). An operator
may input a preselected torque level
82 into the input device
68.
The preselected torque level
82 is carried through the conduit
64
to the control system
50A. The control system
50A may transmit output
data
72 through conduit
70 to the output device
74. The output
data
72 may include the preselected torque level
82 or the output
torque level
84 from the output shaft
18. The output device
68
may be any suitable device (e.g., screen, liquid crystal display, etc.). The control
system
50A sends a switch control signal
86 through a conduit
88
to the switch
15A. The operator uses the activation trigger
16 to
turn the switch
15A on and the control system
50A turns the switch
15A off when the preselected torque level
82 is reached in the output
shaft
18.
FIG. 4 shows another embodiment of a power tool
10B similar to the power
tool
10A, except the control system
50A, the output device
74,
the input device
68, and a switch
15B are external to the housing
11 of the power tool
10B. The switch
15B is in line with the
supply line
17. The switch
15B may include (e.g., a shut off valve,
a solenoid valve, an electrical switch, a slide valve, a poppet valve, etc.). As
in the power tool
10A, the preselected torque level
82 is entered
into the control system
50A using the input device
68. The control
system
50A turns off the switch
15B when the output torque level
84 reaches the preselected torque level
82. The switch
15B
stops the flow in the supply line and the motor
12 stops.
FIG. 5 shows a schematic view of the steps in using the power tool
10A,
10B. In step
90, an operator inputs the preselected torque level
82 into the input device
68. In step
92, the preselected torque
level
82 is displayed on the output device
74. In step
94,
the motor
12 is turned on using the activation trigger
16. In step
96, the control system
50A using the ferromagnetic sensor
30,
measures the output torque level
84. In step
98 the control system
50A displays the output torque level
84 on the output device
74.
In step
100, the control system
50A turns off the motor
12
when the output torque level
84 in the output shaft
18 reaches the
preselected torque level
82.
While this invention has been described in conjunction with the specific embodiments
outlined above, it is evident that many alternatives, modifications and variations
will be apparent to those skilled in the art. Accordingly, the preferred embodiments
of the invention as set forth above are intended to be illustrative, not limiting.
Various changes may be made without departing from the spirit and scope of the
invention as defined in the following claims.
While embodiments of the present invention have been described herein for purposes
of illustration, many modifications and changes will become apparent to those skilled
in the art. For example, the torque transducer
30 may include any suitable
sensor (e.g., ferromagnetic, resistive, optical, inductive, etc.). Accordingly,
the appended claims are intended to encompass all such modifications and changes
as fall within the true spirit and scope of this invention. In particular, it should
be noted that the teachings of the invention regarding the determination of torque
using measurements from a torque transducer are applicable to any power impact
tool and that the above description of the preferred embodiment in terms of a mechanical
impact tool and, more particularly, to a mechanical impact wrench should not be
considered as limiting the invention to such devices.
*
