BACKGROUND OF THE INVENTION
This invention relates to an interchangeable fastener supply
device according to claim 1 and a method for preparing a tool according to claim
8. An example of an interchangeable fastener supply device is disclosed in EP 1005958.
Portable combustion powered tools for use in driving fasteners
into workpieces are described in commonly assigned patents to Nikolich, U.S. Patent
Nos. Re. 32,452; 4,403,722; 4,483,473; 4,483,474; 5,197,646 and 5,263,439. Similar
combustion powered nail and staple driving tools are available from ITW- Paslods
under the IMPULSE® brand.
Such tools incorporate a generally pistol-shaped tool housing
enclosing a small internal combustion engine. The engine is powered by a canister
of pressurized fuel gas also called a fuel cell. A battery-powered electronic power
distribution unit or electronic sending unit produces the spark for ignition, and
a fan located in the combustion chamber provides for both an efficient combustion
within the chamber, and facilitates scavenging, including the exhaust of combustion
by-products. The engine includes a reciprocating piston having an elongate, rigid
driver blade disposed within a piston chamber of a cylinder body.
A wall of the combustion chamber is axially reciprocable
about a valve sleeve and, through a linkage, moves to close the combustion chamber
when a workpiece contact element at the end of a nosepiece, or nosepiece assembly,
connected to the linkage is pressed against a workpiece. This pressing action also
triggers the introduction of a specified volume of fuel gas into the combustion
chamber from the fuel cell.
Upon the pulling of a trigger, which causes the ignition
of the gas in the combustion chamber, the piston and the driver blade are shot downward
to impact a positioned fastener and drive it into the workpiece. As the piston is
driven downward, a displacement volume enclosed in the piston chamber below the
piston is forced to exit through one or more exit ports provided at a lower end
of the cylinder. After impact, the piston then returns to its original or "ready"
position through differential gas pressures within the cylinder. Fasteners are fed
into the nosepiece barrel from a supply assembly where they are held in a properly
positioned orientation for receiving the impact of the driver blade. The fasteners
are then propelled through the length of the barrel by the driver blade, exiting
the barrel at the workpiece surface. Force of the driver blade and the momentum
of the fastener drive the fastener to penetrate the workpiece.
There is considerable shock and vibration that is absorbed
by the tool with each firing of the combustion chamber. Rapid movement of the piston
within the cylinder due to the expansion of combustion gases and the force of the
driver blade on the workpiece tend to propel the tool away from the fastener as
it is driven into the workpiece. Immediately following firing of the tool, the hot,
expanded gases are purged from the combustion chamber, the cylinder rapidly contracts,
drawing the driver blade back up into the tool within a fraction of a second, tending
to recoil and propel the tool in the opposite direction. These forces put large
stresses on the housing and all parts of the tool, causing wear where materials
flex or parts abrade on each other.
Stresses as described above are particularly acute when
short fasteners are driven by the tool. In many applications, long nails are used
predominantly. When driving long nails, more of the force from the power source
and exerted through the driver blade is absorbed by the nail as it penetrates the
workpiece. As the fastener is driven deeper, additional force is needed to overcome
friction between the fastener and the workpiece as the surface area between the
two surfaces increases. Short fasteners require less force to completely penetrate
the workpiece, so the excess power is absorbed by both the user and the tool. In
the extreme, a blank fire, whereby the tool is fired when no fastener is present
to absorb any of the shock, puts tremendous stress on the tool, possibly shortening
the useful life of the tool.
Control of energy output to a combustion-powered tool is
disclosed in U.S. Patent No. 5,592,580 to Doherty et al. A voltage divider includes
a settable resistance, either a potentiometer or two parallel, fixed resistances
that can be alternatively selected, and is used to provide a setpoint voltage. This
patent also discloses changing the fan speed in response to light transmission between
a phototransmissive diode and a photoreceptive transistor. Thus, it discriminates
between fasteners of various lengths, and selected the voltage to the fan depending
on the position of the photoelectric switches.
However, reduction in fan speed alone has been unsuccessful
in producing a tool that fires consistently at low power. Use of the fan to exhaust
the combustion products serves two primary purposes. It produces turbulence in the
vicinity of the combustion chamber, promoting heat transfer to cool the tool after
firing, as well as mixing of the combustion gases with fresh, oxygenated air. Mere
reduction in the fan speed limits both the cooling and replenishment of oxygen in
the combustion chamber. When combustion products remain in the combustion chamber
in the subsequent combustion cycle, the fuel-to-air ratio may become difficult to
control. After several firings, tools running at a low fan speed can have insufficient
oxygen to support combustion.
The use of a metering valve to control the flow of fuel
into the chamber is disclosed in U.S. Patent No. 5,752,643 to MacVicar et al. and
in U.S. Patent No. 6,123,241 to Walter et al. This invention teaches the use of
the metering valve to control the fuel-to-air ratio more precisely to improve the
efficiency of combustion. However, use of metering valves with high pressure fluids
used in very small quantities are difficult to control.
US 6,123,241 teaches further a fastener magazine content
switch to provide a signal if the content of the fastener magazine falls below a
Thus, there is a need in the art for a power tool that
is able to efficiently reduce the primary power expended when short nails are in
use. There is also a need for a tool that varies the power expenditure automatically,
without the need to change settings or switches by the user. In a tool that varies
the primary power by changing the fan speed, there is an additional need for an
improved system for evacuating the combustion gases following combustion so that
they do not built up, interfering with proper fuel to air ratios for efficient combustion.
SUMMARY OF THE INVENTION
These and other needs are met or exceeded by the present
invention which features an improved system for positioning a tool on a workpiece
for precise placement of the fasteners and automatically adjusting the power output
of a tool based upon the length of the fastener.
More specifically, the present invention provides a tool
for driving fasteners into a workpiece, including a housing, a nosepiece at least
partially defining a channel through which fasteners are expelled, a fastener supply
removably attachable to said tool and supplying the fasteners to the channel, and
a workpiece contact element. There is a first alignment mechanism on the nosepiece
and a second alignment mechanism on the workpiece contact element. The second alignment
mechanism engages the first mechanism for alignment to maintain alignment between
the workpiece contact element and the nosepiece. A threaded adjusting member located
on the workpiece contact element and a threadable adjustable mechanism on the nosepiece
are configured engage with each other, such that movement of the workpiece contact
element due to rotation of the threadable adjustable mechanism causes the first
alignment mechanism to engage the second alignment structure.
The tool has a sensor held by the housing and a detector
within the fastener supply configured to sense the length of the fasteners and communicate
the length to the sensor. One embodiment is the detector is a lever that rotates
in response to a force exerted by fasteners that exceed a predetermined length.
The tool described above allows for more precise placement
of fasteners using a workpiece contact element that is easily interchangeable with
standard workpiece contact elements, but is held securely on the nosepiece. Consistent
placement of the fasteners requires, in part, that the workpiece contact element
housing not move relative to the nosepiece during firing of the tool. Configuration
of the present workpiece contact element limits movement of the apparatus in several
directions while keeping installation fast and simple.
Further, the present method and apparatus also automatically
adjusts for the length of the fastener. A detector on the tool provides an signal
as to the fastener length that is used to vary the power. The tool is saved from
wear and tear due to stresses absorbed when small fasteners or blanks are fired.
Reduction of power reduces the materials that flex or abrade on each other when
fired. The present system does not require the user to remember to change a setting
or manipulate a manual lever when changing to a magazine with differently sized
BRIEF DESCRIPTION OF THE DRAWINGS
DETAILED DESCRIPTION OF THE INVENTION
- FIG. 1 is a perspective drawing of the present tool with the alternate embodiment
of the workpiece contact element, with a portion of the housing cut away to show
the fan and combustion chamber;
- FIG. 2 is a fragmentary side view of a portion of the circuit board of the tool
of FIG. 1, with the electrical connections to the battery, the fan motor and magazine
sensor represented schematically;
- FIG. 3 is a perspective view of the magazine, nosepiece and workpiece contact
- FIG. 4 is a fragmentary view of a portion of the magazine and the sensor showing
the interaction between the lever and the sensor, with the lever in the first position;
- FIG. 5 is a top view of the magazine and sensor of FIG. 4 with the lever in
the second position;
- FIG. 6 is a fragmentary, vertical cross-sectional view of a magazine and nosepiece
showing an alternate embodiment of the detector;
- FIG. 7 is a bottom perspective view of the workpiece contact element;
- FIG. 8 is a top perspective view of the workpiece contact element; and
- FIG. 9 is a bottom perspective view of an alternate embodiment of the workpiece
contact element with a fixed shoe.
Referring to FIG. 1, a power tool, generally designated
10, is designed to utilize a plurality of power levels from a combustion by reducing
the power to a fan motor 12 prior to firing of the tool, then returning it to full
power immediately following combustion. The power tool 10 for use with the present
power control system includes a housing 14 and a combustion chamber 16, that produces
primary power to drive fasteners 20, held within the housing. A workpiece contact
element 22, adjustably threadable to a threadable adjustment mechanism 24 on a nosepiece
26, moves to close the combustion chamber 16 through a linkage (not shown) when
the workpiece contact element 22 is pressed against a workpiece 32. The fasteners
20 are fed to a channel 34 at least partially defined by the nosepiece 26 from a
supply assembly 36, such as a removably attachable magazine. A power control system,
the interchangeable nosepiece 26 and components of the work contact element 22 enable
the tool 10 to be converted conveniently for use with a plurality of different types
of fasteners 20. Directional references used herein are to be interpreted when the
tool 10 is oriented as in FIG. 1 and are not intended to limit the invention in
Referring now to FIGs. 1 and 2, fuel is provided to the
combustion chamber 16 from a fuel cell 38 and mixed with air in an appropriate ratio.
When the tool 10 is fired, the mixture in the combustion chamber 16 is ignited and
rapidly burned, generating carbon dioxide, water vapor and other gases under high
pressure. The gases push on a piston (not shown), pushing it downward and driving
an attached driver blade 40 to contact a fastener 20 in the channel 34 and expel
it from the channel. Following combustion, the spent combustion gases are purged
from the combustion chamber 16 in preparation for the next firing using a fan 41
driven by the fan motor 12, which is powered by a secondary power source, such as
a battery 42, in the vicinity of the combustion chamber.
Several different types of fasteners 20 are used with power
tools 10. Frequently, the fasteners 20 are nails having round heads, square heads
or clipped head nails, also known as "D" shaped heads. For the fasteners 20, the
use of the nails with either the heads centered or offset on a shank are contemplated.
Offset, round head or clipped nails are a first type of fastener 20 that is commonly
used in, i.e., when directly connecting two pieces of wood. A second type of the
fastener 20, used frequently with metal strapping or support brackets 44 having
prepositioned openings 46, is a full round head, hardened nail, such as Positive
Placement® nails by ITW- Paslode of Glenview, IL. These two fastener types
are discussed herein as examples of the fasteners 20 with which this invention is
used, and are not intended to limit this invention, in that any type of fastener
which may be driven by the tool 10 is suitable for the present invention.
The present power control system automatically varies the
primary power to the tool 10 prior to driving the fastener 20 and returning to full
power following driving of the fastener, whereby the power varies in relation to
the length of the fastener. Discrimination between the fasteners 20 that are driven
with full power compared to those driven with reduced power is determined by many
factors. For most situations, 1S inch nails 20 can be driven with approximately
50% power compared with nails of about 2S to 3 inches. For convenience of discussion,
1S inch nails are referred to as short fasteners 20 while 2S to 3 inch
nails are known as long fasteners. For the purposes of this discussion, only two
fastener lengths, short and long, will be considered, however it is contemplated
that any number of possible distinctions in fastener lengths are suitable.
Turning to FIG. 3, a detector 50 in the magazine 36 senses
the length of the fastener 20. In one embodiment, the detector 50 is mechanical,
such as a pivoting lever. The lever 50 is selectively displaced depending on the
length of the fastener 20. While several suitable mechanical detectors 50 are discussed
in detail below, this invention is not to be construed as to being limited to mechanical
detectors 50. Optical detectors, infrared detectors, magnetic, sonic, or any other
type of detector 50 is suitable that can discriminate between fasteners 20 having
different lengths compared to a predetermined length.
The lever-type detector 50 discussed above is shown in
detail in FIGs. 4 and 5. The detector 50 includes a lever arm 52 and a pin 54. A
pivot ring 56 surrounds the pin 54 and provides a point about which the lever arm
52 freely rotates. Projecting from one side of the pivot ring 56, there is an actuating
arm 60 supporting an offset plate 62. The plate 62 is in registry with, and contacts
a sensor 64 on the tool 10. Opposite the actuating arm 60 is a sensing arm 66, which
includes a channel face 70 and a positioning face 72. At least a portion of the
positioning face 72 extends into the path of the long fasteners 20. The lever arm
is positioned at a bottom 74 of the magazine 36 so that all of the fasteners 20
easily pass over the actuating arm 60 as they move toward the channel 34. A top
surface 76 of the sensing arm 66 slopes upwardly toward the fasteners 20 from the
pivot ring 56 to the channel face 70. The maximum height of the sensing arm 66 at
the channel face 70 is governed by the predetermined length of the fastener 20 that
the detector 50 is intended to distinguish. The sensing arm 66 of this embodiment
must be tall enough to contact the fastener 20 of a predetermined length as it passes
over the lever.
As seen in FIG. 4, the lever is in a first position. When
the sensor 64 is a push button that is biased toward the magazine 36, the biasing
force generated by the button holds the lever in this position. Optionally, the
button 64 is shielded by a strip of spring steel (not shown) between the button
and the magazine 36. The strip protects the button 64 during installation and removal
of the magazine 36 and provides an additional biasing force toward the magazine
if needed. In this position, the short fasteners 20 pass over the lever entirely
and enter the channel 34 without contacting the lever.
However, when long fasteners 20 are used, a portion of
the fastener contacts the positioning face 72 of the lever, moving it to a second
position. A lower portion 80 of the fastener 20 pushes against the positioning face
72 of the sensing arm 66, causing it to pivot in the direction indicated by arrow
A. In this position, the channel face 70 moves from blocking a portion of the channel
34, to a position allowing the long fasteners 20 to pass. Pushing the sensing arm
66 in direction A causes the lever to pivot about the pin 54, pushing the actuating
arm 60 in the opposite direction as indicated by arrow B. This movement pushes the
plate 62, which is already in registry with the button 64, against the button, overcoming
the biasing force exerted by the button against the plate and causing it to be actuated.
A second embodiment 250 of the detector is seen in FIG.
6. Working in basically the same fashion as the detector 50 of FIGs. 4 and 5, the
detector 250 moves in a direction C, pivoting about a point 252 on one end of the
detector rather than a central pivot point. In this case, the detector 250 is spring
biased upward, toward the fasteners 20. The short fasteners 20 do not move the detector
250, leaving the detector in a first position. But when the long nails pass by it,
they push the sensing face 256 of the detector 250 down to a second position shown
in FIG. 6. The sensor 64 (not shown) occupies any suitable location where it can
be actuated by the detector 250. Preferably, the sensor 64 is located below the
first position of the detector 250, so that it is triggered by an actuating face
258 of the detector when the it moves from the first position to the second position.
In yet a third embodiment (not shown), alternate yet equivalent
of the detector 50, the detector pivots about a point and rotates, but the actuating
face operates a cam linkage to a plate. The cam linkage transforms movement of the
detector through the vertical plane to lateral motion by the plate, so that depression
of the detector by long nails causes the sensor button to be depressed by the plate.
Referring to FIGS. 2 and 4, the detector 50 sends a signal
to communicate to the sensor 64 information in response to the length of the fastener
20 in the magazine 36. The sensor 64 then communicates the fastener length to a
controller 82. It is contemplated that the absence of a signal is one particular
type of signal. Suitable types of the signal generating devices that are useful
with this type of invention include mechanical linkages, electrical signals, optical
signals, sounds, and the like. In the embodiment of the tool 10 shown here, the
detector 50 is the lever that is biased to a first position by the button 64 and
rotates to a second position when the fasteners 20 are at least a predetermined
length. The position of the lever depresses the button 64 to produce a signal that
has a first value when the button is not depressed and has a second value when the
button is depressed. In moving from the first position to the second position, the
detector 50 depresses the button 64, causing a change in the electrical circuit
that depends on whether the button 64 is depressed or not. Thus, when short fasteners
20 are being used, the signal has the first value, but if the fasteners are long,
the signal changes to the second value.
It is to be understood that fastener length is not the
only factor that determines the power required to fully drive the fastener 20 into
the workpiece 32 (FIG. 1). In this discussion, a full power and a reduced power
of approximately 50% of full power are discussed for simplicity. However, it is
to be understood that many other power levels are suitable for use in this invention,
either as replacement for or in addition to those disclosed above. Additional power
is needed when driving fasteners 20 into hard woods or pressure treated wood compared
to soft wood. Some fasteners 20, such as ringed nails, require more power to drive.
It is contemplated that the distinction between the power generated at full power
and the power generated at one or more reduced power settings is dependant on the
application for which the tool is intended and the materials to be used. Use of
a continuous, but not necessarily linear, power reduction is also contemplated.
It is contemplated that the use of some fastener types
will not necessitate varying the power output from the tool as the fastener length
changes. In this case, it is contemplated that magazines 36 for this particular
fastener type will not have a detector, and the magazine will have a solid panel
that holds the button depressed at all times.
Once the desired reduced power level is chosen as discussed
above, a fan speed is determined to produce the reduced power level. Power varies
directly, but not necessarily linearly, with fan speed until full power is reached.
When there is complete mixing of the air and fuel and the spent combustion gases
are essentially completely evacuated from the combustion chamber 16 following combustion,
increasing the fan speed generates little or no significant increase in power. The
fan speed changes somewhat as the battery discharges. One average reduced fan speed
is suitable for use over the whole battery cycle, or, preferably, the fan speed
can fluctuate with the battery charge.
Referring back to FIGs. 1 and 2, the fuel and the air are
added to the combustion chamber 16 in an appropriate ratio prior to combustion when
the workpiece contact element 22 is engaged upon the workpiece 32 and the tool 10
is depressed prior to firing. The fuel is supplied to the tool 10 from the fuel
cell 38, and then flows to a metering valve (not shown), through a fuel line (not
shown) and into the combustion chamber 16. The fan 41, powered by the fan motor
12, generally located on a side of the combustion chamber 16 opposite the driver
blade 40, draws air in and promotes turbulence. When the combustion chamber 16 is
closed, turbulence mixes the gases contained therein, encouraging them to burn more
efficiently. Continued movement due to momentum of the fluids during combustion
propagates the flame front more quickly. Thus, low fan speeds, after engagement
of the workpiece contact element 22, while the fuel and air are being mixed, but
prior to combustion, reduce the primary power from the combustion chamber 16 by
reducing the efficiency of combustion.
Following combustion, however, it is important to evacuate
the spent combustion gases from the combustion chamber 16. Immediately following
combustion, the fan speed is returned to full power for an evacuation period in
preparation for the subsequent cycle of mixing and combusting of fuel. Preferably
the evacuation period is from one to about five seconds in length, however, a wide
range in the evacuation periods is contemplated. The evacuation period need not
be a fixed length, but can last until the subsequent engagement of the workpiece
contact element 22. One embodiment of the invention utilizes an evacuation period
between one and three seconds.
Still referring to FIG. 2, quick reduction in speed of
the fan 41 is accomplished using an optional braking system 84. Any method of shorting
the fan motor 12 is contemplated for use as the braking system 84. One embodiment
of the braking system 84 includes a transistor 86 wired across the fan motor 12
that shorts the motor when the transistor is activated. Selection of the appropriate
transistor 86 will be obvious to those skilled in the art. In place of the transistor
86, a relay (not shown) could also be used to short the fan motor 12.
It is also contemplated that the length of the evacuation
period not be used to slow the work pace of the user. If the workpiece contact element
22 is engaged upon the workpiece 32 prior to the expiration of the evacuation period,
the braking system 84 is used to immediately reduce the fan speed after a shortened
Once the fan 41 reaches the desired speed, the speed is
maintained at a lower level by reducing power to the fan motor 12. Any method of
reducing power to a DC motor is suitable, including reduction in the voltage or
pulsing power to the motor, turning it on and off in rapid bursts to achieve the
average desired fan speed. Use of resistance to alter the fan speed is contemplated,
by selection of two or more parallel resistances. Pulse-width modulation of the
battery voltage is the preferred method of maintaining the low speed.
If, as preferred, the controller 82 is an electronic microcontroller,
execution of a software program stored in the microcontroller is one way of varying
in the fan speed based on the signal, applying the braking system 84 and modulating
the power to the fan 41. The use of microcontrollers 82 is well known to artisans
for such uses. The power to the fan motor 12 is output from the microcontroller
82, while information as to the fan speed is input to the microcontroller from an
Analog to Digital Converter ("ADC") 88. The ADC 88 is preferably built into the
controller 82, but use of a stand alone ADC is also contemplated.
A set of simple instructions in the form of programming
in the microcontroller 82, directs the microcontroller how and when to vary the
power to the fan 41. A discussion of one possible instruction set is discussed below
to exemplify one embodiment of this control system, however, it is to be understood
that many such instruction sets are possible, and many variations in this control
scheme will be obvious to those skilled in the art of designing control systems.
The exemplary control system disclosed below varies the power duty cycle based on
the battery voltage and includes the optional braking system 84. Numerical values
are provided, such as the fan speed, times and frequencies, are given as an example
only and are not meant to limit the invention. The number, size and shape of fan
blades 89 (FIG. 1) will contribute to the number of revolutions per minute necessary
to produce a given turbulence and the time needed to increase or reduce fan speed.
The size and shape of the combustion chamber 16 and the amount of fuel used per
charge determines how much turbulence is needed to evacuate the combustion chamber
16. The exact electronics of the microcontroller 82 affects the frequency of the
pulse width modulation.
Continuing to refer to FIG. 2, the microcontroller 82 of
this embodiment has internal components for the analog to digital converter ("ADC")
88 and Pulse Speed Width modulated output. Adjusting the duty cycle of the PWM drive
motor controls the fan speed. PWM output runs at 7843 Hz (127.5 µS) and can
be adjusted in 0.5 µS (0.4%) steps. The PWM duty cycle is increased as the
battery voltage goes decreases to maintain a constant fan speed. Target PWM output
is 5.5 µS for 3000 RPM and 6.0V or 2.0 µS for 1500 RPM at 6.0V.
Speed of the motor 12 is sensed by turning off power to
the motor and measuring the voltage generated by the motor using the ADC 88. A target
voltage is the voltage read by the ADC 88 when the fan 41 is rotating at the target
speed to achieve the desired reduced power setting. The target motor voltage in
this embodiment is 1.4V for 3000 RPM or 0.7 V for 1500 RPM. During start and braking,
a lower motor voltage target is used to compensate for overshoot on start up and
undershoot on braking.
When starting the fan motor 12 in slow speed from a stop,
nominal pulse width modulated duty cycle is calculated based on the battery voltage.
DC power is applied to the motor for 12 mS. If the motor voltage is under 20% of
the battery power, the motor is shorted and operation is halted. Thereafter, a 4
mS testing loop begins whereby the power to the fan 41 is turned off for 165µ
and the motor voltage is read from the ADC 88. If the motor voltage is greater than
or equal to the target voltage, then this loop is exited, otherwise DC power is
restored to the motor and another iteration of the loop begins. When the target
voltage has been reached, pulse width modulation begins using the duty cycle calculated
based on the battery voltage.
Optionally, there is a first shot delay time within which
the tool 10 is normally fired. There is an optional provision in the testing loop
to stall the fan 41 and halt operation if the first shot delay time is reached before
the fan reaches the target speed. This is a safety feature that shuts down operation
if the fan 41 does not begin turning for any reason.
Referring again to FIGs. 1 and 2, engagement of the workpiece
contact element 22 depresses an interlock switch 90 that prevents fuel gas from
being introduced into the combustion chamber 16 and preventing firing of the fastener
20 unless the tool 10 is in contact with the workpiece 32. When the interlock switch
90 is depressed far enough, it triggers the introduction of fuel gas into the combustion
chamber 16, and mixing of the fuel and air begins. Engagement of the interlock switch
90 is a convenient method of triggering reduction in the fan speed if the sensor
64 is released, indicating that reduced power is advantageous.
While the fan 41 is running at the reduced speed, the fan
speed is checked every 246 mS to by the controller 82. To check the speed, the power
output to the motor 12 is turned off, and the voltage of the motor 12 is sampled
using the ADC 88. If the motor voltage is less than 5% of the battery capacity,
the motor 12 is stalled and operation is halted. If the ADC 88 reading is within
two counts of the target voltage, there is no change in the duty cycle. However,
if the ADC 88 reading is more than two counts above or below the target value, the
duty cycle is increased or decreased, as appropriate, to bring the fan motor speed
toward the target value. Following any needed adjustments, power output from the
controller 82 to the motor 12 is resumed.
When the fan speed is reduced from full speed to the reduced
speed, the optional braking system 84 is employed. The fan motor 12 is turned off,
and the PWM duty cycle is calculated based on the reduced fan speed. The brake transistor
86 is activated for 160 mS, shorting the fan motor 12. A second testing loop is
employed to determine when the target brake voltage has been reached. Every 4 mS,
the brake transistor 86 is turned off for 165 mS, and then the motor voltage is
read using the ADC 88. If the motor voltage is less than the target brake voltage,
the controller 82 exits this loop, otherwise, the brake transistor 86 is turned
on again and another iteration of the loop begins. Optionally, there is a time limit
to end the loop if the target motor voltage has not been reached within a reasonable
time. After the target motor voltage has been reached, the PWM motor output begins
using the nominal PWM duty cycle.
Referring now to FIGs. 1, 3, 7 and 8, when using fasteners
20 that benefit from precise placement in the workpiece 32, such as when the metal
bracket 44 with the openings 46 are used, the workpiece contact element 22 has a
housing 91, a swiveling probe 92 and a support 93 for a pivot pin 94. Swiveling
of the probe 92 about the pivot pin 94 allows it to pivot relative to the housing
91 along a radius from the longitudinal axis of the channel 34. The probe 92 depends
from the workpiece contact element 22, and has a tip 96 engagable with the workpiece
32, and a stop surface 98 (FIG. 3). A trough 99 blocks a portion of the channel
34, limiting side-to-side motion of the fastener 32 as it moves through the channel.
The tip 96 has a groove 100 to guide the fasteners 20 into the workpiece 32. Insertion
of the tip 96 into one of the openings 46 and depression of the tool 10 engages
the workpiece contact element 22.
Upon firing of the tool 10, the fastener 20 exits the channel
34 and contacts the groove 100 of the probe 92. The lower end 80 of the fastener
20 (FIG. 4) travels down the groove 100 and into the opening 46 in the workpiece
32 immediately beside the position where the probe 92 is located.
As the fastener 20 enters the workpiece 32, it pushes the
probe 92 out of the opening 46, allowing the head of the fastener 20 to pass the
position where the probe was located without jamming. When the probe 92 is pushed
out of the opening 46, the swiveling probe 92 pivots about the pivot pin 94 until
the stop surface 98 contacts the workpiece contact element 22, limiting movement
of the rotating arm Motion of the probe tip 96 is limited along a radius from a
longitudinal axis of the channel 34. The pivotable probe 92 preferred for use with
this invention is disclosed in U.S. Patent No. 5,452,835 to Shkolnikov.
An alternate embodiment of the workpiece contact element
322, is shown in FIGs. 1 and 9, and is used for general applications. This workpiece
contact element 322 does not have the pivotable probe 92, the support 93 or pivot
pin 94, but rather has a fixed foot 381. At the end of the workpiece contact element
322 is a tip 396, which is set radially outwardly from the channel 34 to allow the
head of the fastener 20 to pass by without jamming.
The workpiece contact element 22 has been made easily interchangeable
in the tool 10 through its engagement with the threadable adjustable mechanism 24.
A first alignment mechanism 102 (FIG. 1) on the nosepiece 26 is configured for engagement
with the workpiece contact element 22. One embodiment of the threadable adjustable
mechanism 24 is a threaded adjusting barrel member 103 on the nosepiece 26. A threaded
member 104, such as a screw, extends from the workpiece contact element 22 diametrically
opposite the probe 92 and engages with the threadable adjustable mechanism 24. The
barrel 103 of the threadable adjustable mechanism 24 is rotatable upon engagement
with threads 106 of the threaded member 104. When the threaded member 104 is aligned
with the threadable adjustable mechanism 24 and the barrel 103 is rotated, the rotational
motion is converted to linear motion of the workpiece contact element 22, allowing
the workpiece contact element 22 to be securely attached to the nosepiece 26 at
an appropriate height.
The workpiece contact element 22 also includes a second
alignment structure 108 configured for slidingly engaging the first alignment mechanism
102 on the nosepiece 26. Any first and second alignment structure 102, 108 is contemplated
for maintaining alignment between the workpiece contact element 22 and the nosepiece
26 after numerous firings of the tool 10. Forces generated by movement of the probe
92 radially away from the channel 34, and the general recoil of the tool 10 following
Bring, tend to move the workpiece contact element 22 relative to the nosepiece 26.
These forces will have the greatest effect when there is a large moment arm between
the area where the force is applied and the area where the workpiece contact element
22 is secured, as when the threadable adjustable mechanism 24 and threaded member
104 are on opposite sides of the workpiece contact element 22 from the probe 92.
Preferably, the first and second alignment structures 102, 108 are a tongue and
groove, a boss and a cover, a pin and a channel, a pair of abutting shoulders, a
capturing system or any other system for maintaining alignment between the nosepiece
26 and the workpiece contact element 22. It is not important which portion of the
alignment structure resides on the nosepiece 26 and which portion resides on the
workpiece contact element 22. In this preferred embodiment, the first alignment
mechanism 102 is a groove on the nosepiece 26 and the second alignment structure
108 is a tongue on the workpiece contact element 22.
This preferred embodiment uses a second alignment mechanism
to further limit motion of the workpiece contact element 22 relative to the nosepiece
26 when the tool 10 is fired. At least one tab 110 on the housing 91 wraps around
to enclose and capture the nosepiece 26, sliding over it as the workpiece contact
element 22 is installed.
Initialization of the threaded member 104 into the threadable
adjustable mechanism 24 places the tongue 108 below, but in registry with the groove
102. The preferably two tabs 110 are also aligned to slidingly capture the nosepiece
26. As the threaded adjusting mechanism 24 is turned, the threaded member 104 is
drawn upward, so that the probe 92 approaches the exit of the channel 34, the nosepiece
26 is received by the housing 91 and tabs 110 and the tongue 108 approaches the
groove 102. Continued rotation of the barrel 103 draws the tongue 108 into the groove
102. This mounting mechanism holds the workpiece contact element 22 securely in
place, horizontal motion being severely limited by the tongue 108 and the groove
102, as well as the tabs 110, while vertical motion in limited by the engagement
of the threaded member 104 in the threaded adjusting mechanism 24.
The relationship between all elements of this invention
is understood when converting the tool 10 from use of the first type fastener 20
to the second type fastener.
It is to be understood that changing of the workpiece contact
element 22 and the magazine 36 can be done in any order.
Referring to FIGs. 1, 3 and 7, the alternate workpiece
contact element 322, is removed from the tool 10 by turning the barrel 103 of the
threadable adjustable mechanism 24 in a direction to lower and eventually disengage
the threaded member 104. After removal of the alternate workpiece contact element
322, the workpiece contact element 22 with the probe 92 is placed with the threaded
member 104 aligned in the threadable adjustable mechanism 24 and the adjusting mechanism
is turned to engage the threads 106. Additional turning of the adjusting mechanism
24 draws the workpiece contact element 22 upward, capturing the nosepiece 26 with
the tabs 110 and engaging the tongue 108 in the groove 102.
Now referring to FIGs. 4 and 5, prior to installation of
the magazine 36 of this invention, the second type of the fasteners 20 are loaded
into the magazine. As the fasteners 20 move through the interior of the magazine
36, the fasteners pass the detector 50. If the long fasteners 20 are loaded into
the magazine 36, they pass over the actuating arm 60, but are pressed against the
positioning face 72 of the sensing arm 66, causing it to rotate about the pivot
pin 54. Rotation of the sensing arm 66 in direction A causes the actuating arm 60
to rotate in direction B, depressing the button 64. As soon as the button 64 is
depressed, the signal to the controller 82 (FIG. 2) tells it to maintain full power
Referring now to FIGs. 2 and 4, if short fasteners 20 are
loaded, the detector 50 does not move due to the length of the fasteners and the
button 64 is not depressed. The signal to the controller 82 initiates steps to reduce
power to the fan 41 while the air and fuel are being mixed in the combustion chamber
16. As the fan 41 starts up, the controller 82 applies power to the fan 41 in short
bursts. Between the bursts, the controller 82 reads the ADC 88 to determine the
voltage of the motor 12, thereby determining the present speed of the fan. If the
fan 41 has not reached the target speed, the controller 82 again applies power and
checks the fan speed. When the fan 41 attains the target speed, it is maintained
at that speed by the pulse width modulation of the power to the fan until the tool
10 is fired.
Following firing, the fan 41 is returned to full power
to evacuate the combustion gases from the combustion chamber 16. The fan 41 is held
at full power for up to 5 seconds, then the fan is reduced to low speed. If the
workpiece contact element 22 is engaged prior to reduction of fan speed, the braking
system 84 is immediately engaged to slow the fan speed to the target speed.
Referring to FIGS. 1, 2 and 4, a method of driving the
fasteners 20 into the workpiece 32 begins by passing the fasteners 20 past the detector
50 in the magazine 36. The detector 50 identifies the length of the fastener 20
and activates the sensor 64 to produce or change a signal. In one embodiment, the
detector 50 is biased in the first position, but rotates to a second position if
the fasteners 20 are at least a predetermined length. Rotation of the lever depresses
a button 64 when the lever moves from the first position to the second position.
The sensor 64 is produced having a first value when the button is not depressed
and the signal is a second value when the button 64 is depressed. After passing
the detector, the fasteners 20 are urged through the magazine 36 to the channel
Pressing the tool 10 to the workpiece 32 engages the workpiece
contact element 22, causing fuel to be introduced into the combustion chamber 16.
The primary power from the combustion chamber 16 is varied in relation to the signal,
causing the driving of the fastener 20 into the workpiece 32 at a power relative
to the length of the fastener. Following combustion of the fuel, the primary power
is returned to full power and purging combustion gases from the combustion chamber.
Variation in the primary power can be caused by varying
the power to a fan 41 from a secondary power source 42, changing the speed of the
fan and creating turbulence in the vicinity of a combustion chamber 16. The power
to the fan 41 is suitably varied by executing programming with an electronic controller
82. The programming is an instruction set that includes reducing the speed of the
fan 41, maintaining the reduced speed until the driving of the fastener 20 and returning
the fan to full speed following the driving of the fastener.
Varying of the fan speed suitably includes additional options.
The braking system 84,is optionally applied to the fan 41, such as activating the
transistor 86 wired across the fan motor to short it. Maintaining the reduced fan
speed is done by modulating pulses of secondary power to the fan 41, by reducing
the voltage or by selecting between a plurality of selectively grounded resistances,
by use of photoelectric switches, or by mechanical linkages. Preferably, the modulating
step is adjusted as the battery 42 is discharged.
While a particular embodiment of the present system for
an improved positioning system and fastener supply for a power tool has been shown
and described, it will be appreciated by those skilled in the art that changes and
modifications may be made thereto without departing from the invention in its broader
aspects as set forth in the following claims.