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CROSS-REFERENCE TO OTHER APPLICATIONS
The present application is related to a copending application of the common
assignee, U.S. Ser. No. 822,166 filed even date herewith, which
application includes an alternate design of a similar type improved
trigger switch.
BACKGROUND OF THE INVENTION
Trigger switches for power tools, such as drills, are either of the on-off
or the speed control type with the speed being variably responsive to the
amount of trigger depression. Whether the trigger switch is assembled in a
plastic case or the housing of the power tool it will usually include a
side lock button which coacts to lock the trigger in the desired position.
The side lock button is inconvenient to operate, is susceptible to
inconvenient use, accidental misuse or breakage, and has a limited range
of speed setting for speed control switches.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved
quick lock-release mechanism for a trigger switch which overcomes the
prior art disadvantages; which is simple, economical, and reliable; which
is quick and easy to lock or release; which is selectivly lockable over a
wide range of variable speed control settings; which mechanism includes a
spring common to the trigger switch and lock-release mechanism; which
spring is nested in a cavity formed in the trigger; which mechanism
includes interacting high friction surfaces formed on the locking member
and the trigger; and while mechanism includes a high friction surface on
the trigger which is of greater length than the high friction surface on
the locking member.
Other objects and advantages will be apparant from the following
description of the invention and the novel features will be particularly
pointed out hereinafter in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
This invention is illustrated in accompanying drawings in which:
FIG. 1 is a side elevational view of a power tool, such as a drill,
embodying the present invention.
FIG. 2 is a side elevational view, partly in section, of the trigger switch
of the present invention mounted in the handle, with only the rear portion
thereof shown, with the switch in the "off" position, the locking member
disengaged and the reversing switch interlocked in the forward position.
FIG. 3 is a side elevational view, partly in section, showing the trigger
switch of FIG. 2 in the "on" position, the locking member engaged and the
reversing switch interlocked in the reverse position.
FIG. 4 is a top plan view taken along lines 4--4 of FIG. 2.
FIG. 5 is a top plan view taken along lines 5--5 of FIG. 2.
FIG. 6 is an elevational view taken along lines 6--6 of FIG. 2.
FIG. 7 is a schematic circuit diagram of the improved trigger switch.
DESCRIPTION OF THE INVENTION
A power tool, such as a portable power drill 10 is shown in FIG. 1
embodying the present invention. The drill 10 includes an electric motor
11 having a field core 12 disposed about an armature 13 affixed to an
armature shaft 14 which carries a commutator 16 engaged by a brush
assembly 18. The armature shaft 14 is journaled in a pair of spaced
bearings 20, and has a drive pinion 22 formed at its forward end. The
pinion drives a gear train 24 and a driven spindle 26, the front of which
exits the drill housing 28 to be threadedly connected to a chuck 30 which
is adapted to drive a suitable bit or implement (not shown) that comes
into engagement with the work. The motor 12 is journaled in the housing 28
as shown in FIG. 1 which is preferably of a clam shell construction as
indicated in FIGS. 4 and 5 wherein a support portion 32 and a cover
portion 34 are suitably connected to each other as by screw means 36
illustrated in FIG. 1 extending through the cover portion 34 of the
housing 28 to be threadedly connected to the support portion or separate
nut means (not shown) to form what is commonly termed a clam shell
housing. The housing 28 has an integrally formed pistol grip handle 38
which receives an electric cord 40 depicted in FIGS. 1 and 9 that in turn
is connected through a trigger switch 42 which is in circuit with the
motor 12 as will be described more fully hereinafter under the schematic
circuit diagram of FIG. 7.
In assembling the drill 10, the cover portion 34 will be removed from the
support portion 32 of the housing 28 to permit easy access and visibility
of all the drill components particularly those included in the trigger
switch 42.
The improved trigger switch 42 has a printed circuit (PC) board 44
illustrated in FIG. 2, the face side 46 of which carries the discrete
devices which are suitably electrically connected through the PC board 44
to the opposite side of the PC board 44, and in circuit with various PC
conductor paths 48 some of which are shown by the dotted line
representation. The PC board 44 is disposed to be connected in the handle
38 either by being entrapped between the handle halves 32 and 34 or by
means of suitable bent tabs, screw fasteners or the like.
A trigger 50 is slidably affixed to the PC board 44 by a rear mounting
strap or bracket 52 and a front mounting strap or camming bracket 54, the
top 56 of which is tapered to extend forwardly and downwardly for purposes
which will be explained more fully hereinafter. Each of the brackets 52
and 54 are connected to the PC board 44 by staking as illustrated in FIGS.
4 and 6 at stake points 58, 58.
The trigger 50 has a front portion 60 which projects from an opening in the
handle as shown in FIG. 1 and is gently curved for comfortable engagement
by the operator's finger. The trigger 50 will be longitudinally depressed
into the handle 38 by the operator. A recess 62, shown in FIGS. 2, 3 and
4, is formed in the top of the forward portion 60 the base of which
extends into the mid-portion 64 and serves as the top surface 65 thereof.
The top 65 is serrated substantially along its entire length to form a
high friction contact surface. A cavity 66 is formed in the mid-portion 64
on the side adjacent the PC board 44 to receive a substantially "U"-shaped
switch contact wiper 68 shown in FIGS. 2, 5 and 6 as having a
substantially flat base 70 which is loaded to the PC board 44 by two
springs 72 and 74 disposed on round bosses 76, 76 formed in the side wall
of cavity 66. The side turned legs of the wiper 68 serve to entrap the
wiper 68 within the cavity 66. A resistance wiper 78 is disposed on the
left most boss 76 shown in FIG. 5 and held in position by the spring 72 as
illustrated in FIGS. 5 and 6. A contact finger 80 is formed integrally
with the wiper 78 and extends downwardly from the open bottom of the
cavity 66 to slidably engage a resistance strip 82 of a
resistance-capacitance (RC) module 83 as shown in FIGS. 2, 3 and 6.
Contact rivets 84, 86 and 88 are connected to the PC board 44 in the path
of travel of the contact wiper 68 and positioned so that upon trigger 50
depression into the handle 38, the wiper 68 will first engage the contacts
84 and 86 and after predetermined further depression of the trigger
contact will be made with the rivet contact 88 for purposes more fully
explained hereinafter. A rear portion 90 of the trigger 50 extends from
the mid-portion 64. The side face of the rear portion 90 facing the PC
board 44 has a shallow recess 92, best seen in FIG. 5, which communicates
with the cavity 66 and is sized to permit that portion of the trigger 50
to travel past, without interfering with, the contact rivets 84, 86 and
88. This is possible because a boss 94 is formed at the rearward end of
the recess 92 to slidingly engage the face 46 of the PC board 44 to the
left of the contact rivet 88. A stop 96 is formed on the inner side of the
trigger 50 adjacent the junction point between the front and mid-portions
60 and 64, respectively, as depicted in FIGS. 4 and 5 to engage the
forward edge 104 of the PC board 44 to limit the maximum depression of the
trigger 50 within the handle 38. A side 98 illustrated in FIGS. 4 and 5
provides continuity for portions 60, 64 and 90 of the trigger 50, extends
adjacent to the PC board 44 and contains the cavity 66 and recess 92
therein.
The trigger 50 has a different width for each portion, with the front
portion 60 having the largest dimension and the mid-portion 64 having the
smallest dimension. The brackets 52 and 54 are sized corresponding to the
adjacent portion of the trigger 50 to be accommodated so that once
assembled to the PC board 44 the trigger 50 will not be accidently
dislodged. The rear portion 90 of the trigger 50 has a vertically
extending projection 100 formed at its rear face side as shown in FIGS. 2,
3 and 4 which acts as a forward stop to engage the top rear edge 102 of
the rear bracket 52 as shown in FIGS. 2 and 3 to prevent excessive forward
motion of the trigger 50. An opening 104 shown in FIGS. 2, 3 and 5 is
formed at the rear of the face side of the rear trigger portion 90 and
leads into parallel horizontal slots, separated by a horizontal rib 106,
with the upper slot 108 being designated for forward motor rotation, and
the lower slot 110 being designated for reverse motor rotation, which
slots are depicted in FIGS. 2 and 3.
A reversing switch 112 is affixed to the PC board 44 in circuit therein.
The reversing switch 112 is a double pole-double throw (DPDT) type, and it
has a slide button 114 used to position it in either forward or reverse.
An actuator 116 having a body portion 118 with a central aperture 120
which is disposed about and in engagement with the slide button 114 of the
reversing switch 112 so that movement of the actuator 116 will place the
reversing switch in an upward position for forward motion of the motor 12
or in a downward position for reverse motion of the motor 12. An interlock
arm 122 extends upwardly from the body 118 to terminate in an inwardly
facing flange 124 shown in FIGS. 2, 3 and 4, which is sized to be
slidingly disposed in the opening 104 to be shifted between slots 108 or
110 of the trigger 50. An actuator arm 126 extends rearwardly, as shown in
FIGS. 2 and 3, from the body 118 to reside within an elongated slot 128
formed in the rear end of the handle 38 for sliding movement therein. The
operator will position the actuator arm 126 in one of two positions, with
the upper position shown in FIG. 2 for forward motion of the motor 12
whereby the flange 124 will be received in the forward slot 108 of the
trigger 50, and the lower position shown in FIG. 3 for reverse motion of
the motor 12 whereby the flange 124 was moved downwardly to be received in
the reverse slot 110. The rib 106 acts to prevent operation of the
reversing switch 112 during operation of the motor 12 upon depression of
the trigger 50. Therefore, once the trigger 50 has been depressed, the
flange 124 will engage the rib 106 to prevent the reversible operation of
switch 118. Thus the actuator 116 can only change the position of the
switch 112 when the flange 124 resides in the opening 104, corresponding
to the trigger switch off position shown in FIG. 2.
A locking or lock-release member 130 is illustrated in FIGS. 2, 3 and 4 and
has a forwardly extending external lever 132 which terminates in a
"T"-shaped handle 134 which extends on either side of the trigger 50 as
shown in FIG. 4. The lever 132 extends externally of the housing 38
immediately above and forwardly of the trigger 50 for convienent operator
manipulation as more fully described hereinafter. The lever 132 is stepped
down at its inner end to form an outwardly facing shoulder 134 adjacent an
offset connection to a midsection 136 shown in FIGS. 2, 3 and 4. The end
wall of the trigger recess 62 defines an inwardly facing shoulder 137. A
spring 138 is disposed in the recess 62 and trapped between with its ends
engaging the facing flanges 134 and 138 of the lock-release member 130 and
the trigger 50, respective. The midsection 136 extends rearwardly to
terminate in a cam shoe 140 the upper surface 142 of which is tapered
corresponding to the tapered top 56 of the camming bracket 54. The lower
surface 144 of the shoe 140 lies horizontally below the lower surface of
the midsection 136 and is serrated to define a high friction contact
surface. The cam shoe 140 of the locking member 130 is entrapped within
the bracket 54, and the tapered surface 142 is in continual contact with
the tapered top 56 of the bracket. With the cam shoe 140 in the rearmost
position, the lower surface 144 will remain out of contact with the upper
serrated surface 65 of the trigger 50. The midsection 136 of the locking
member 130 being disposed in the recess 62 of the trigger 50 wherein the
inner side 146 slidingly engages the side 148 of the recess 62 to guide
the motion of the locking member 130 and limit it to the linear direction.
The spring 138 normally urges the trigger 50 forwardly and the lock-release
member 130 rearwardly so that as viewed in FIG. 2, the trigger seeks to
extend from the handle 38 but is prevented by stop 100, while the
lock-release member 130 is urged into the handle 38 but is limited by a
shoulder 150 abutting a bracket stop 152. Accordingly, the spring 138 will
load the trigger 50 in the "off" position and the lock-release member 130
in the released position out of engagement with the trigger 50.
When the trigger 50 is in the unlocked position shown in FIG. 2, it can be
moved freely through its entire depressed movement wherein it will start
to compress the load spring 138 causing the lock-release member 130 to
abut the bracket stop 152. Completely pulling the trigger 50 into the
handle 38 will not completely compress the spring 138 as illustrated in
FIG. 3 so as to permit free outward locking motion of the lock-release
member 130. With simple trigger 50 pull in motion, upon release the spring
138 will force the trigger 50 to return to its normally "off" position.
Though the present invention is useable with a simple "on-off" switch, it
has been embodied in the trigger-switch 42 which includes speed control
capabilities so as to more completely describe the advantageous results of
the present invention. The extend of trigger 50 depression will determine
the speed at which the drill motor 12 operates with the speed increasing
as the trigger depression increases with the maximum depression of the
trigger 50 being shown in FIG. 3.
To lock the trigger 50 at any desired speed setting of the trigger-switch
42, the trigger 50 will be retracted to obtain the desired speed, which in
the present instance is assumed to be the maximum speed corresponding to
the setting illustrated in FIG. 3, and will be held in that position while
the lock-release member 130 is pushed forwardly. Forward movement of the
lock-release member 130 causes the tapered surface 142 of the cam shoe 140
to slide forwardly and downwardly under the urging of the tapered top 56
of the camming bracket 54 until the cam shoe 140 becomes wedged-locked
under the angled tapered top 56 of the camming bracket 54, thus forcing
the lower surface 144 to seat its serrations into those formed on the top
surface 65 of the trigger 50.
The force exerted by the wedge-lock of the cam shoe 140 of the lock-release
member 130 is sufficient to overcome any restoring force which the spring
138 may exert upon the lock-release member 130. In this instance, the
spring 138 forces are substantially balanced in that the force acting upon
the trigger 50 seeks to maintain the wedge-lock while the force acting
upon the lock-release member 130 seeks to release the member 130. In any
event sufficient force is exerted on or by the cam shoe 140 of the
lock-release member 130 to keep the contact surfaces 65 and 144,
respectively, engaged with each other, and the cam shoe 140 wedged under
the camming bracket 54 to prevent any further forward movement of the
trigger 50, and therefore, any change of speed from the maximum
illustrated in FIG. 3.
To release the lock-release member 130, the trigger 50 is pulled rearwardly
to physically shift the cam shoe 140 rearwardly out from under the angled
face or tapered surface 56 of the camming bracket 54 so as to initiate a
disengagement of the serrated surfaces 65 and 144 whereby the spring 138
will simultaneously (1) push the lock-release member 130 rearwardly to
cause the tapered surface 142 to ride upwardly along the tapered top 56
and away from the serrated top surface 65, and (2) urge the trigger 50
outwardly to the fully extended "off" position shown in FIG. 2. Once the
trigger 50 is free from the wedge-lock and the separation of the serrated
surfaces 65 and 144 is accomplished, the trigger 50 is released and the
spring 138 will restore it to the "off" position. The length of the
serrated top surface 65 of the trigger 50 is substantially twice the
length of the lower serrated surface 146 of the cam shoe 142. This permits
the trigger 50 to be locked in any desired speed setting from "off" to the
maximum speed in the "on" setting.
The switch contact wiper 68 illustrated in FIGS. 2, 5 and 6 is loaded to
the PC board 44 by the contact springs 72 and 74. The wiper 68 is
entrapped in the trigger cavity 66 and will slide with the trigger 50. As
the trigger 50 is pulled rearwardly, the wiper 68 first bridges the rivet
contacts 84 and 86 shown in FIGS. 2 and 6, and in the schematic circuit
diagram of FIG. 7. The various printed circuit conductor paths are
designated generally 48, and are formed on the underside of the PC board
44 as illustrated in FIG. 2, and these conductor paths are shown in
circuit in the schematic of FIG. 7 in which the lines or conductor paths
will still be referred to by the general designation 48, but the
electrical devices or components interconnected by the lines 48 will be
specifically identified. Also, for a better understanding of the
explanation of the electrical operation of the improved trigger switch 42
reference may be had to FIGS. 2 and 7.
Contact 86 is connected to the resistance-capacitance (RC) module 83 and
the anode 158 of the silicon control rectifier (SCR) 160 via one of the PC
conductor paths 48. Likewise contact 84 is connected to the reversing
switch 112, the motor 12 to be controlled, as indicated by the armature 13
and the field 164 disposed within the dotted lines for the motor 12 of
FIG. 7, and one side of the line voltage cord 40 via a PC conductor path
48 and a jumper wire or path also formed on PC board 44, and quick
disconnect terminals 166, 168, 170, 172, 174 and 176. Terminals 166, 168,
170 and 172 serve as output terminals, while terminals 174 and 176 serve
as line cord terminals. Contact 84 connects to the line voltage terminal
174, while the cathode 178 of the SCR 160 is connected to the other line
voltage terminal 176, and therefore, bridging the contacts 84 and 86 will
start the motor 12.
With the SCR 160 in series with the motor 12, the speed can be varied by
the point into every other half cycle of line voltage (when the SCR 160
anode to cathode voltage is positive) at which SCR 160 is triggered into
conduction via the gate 180 of the SCR 160. The gate 180 trigger point is
determined by the position of the resistance wiper 78 on the primary
resistance strip 82 of the RC module 83. The wiper 78 is carried on the
boss 76 of trigger 50 and is connected to line voltage through the spring
72 and wiper 68 to the contact 84. As the trigger 50 moves rearwardly, the
wiper 78 decreases the effective resistance on the module 83 and causes
the capacitor 182 of the module 83 to charge faster. A trigger diode
(diac) 184 breaks down sooner dumping the capacitor 182 charge into the
gate 180 of the SCR 160 and therefore turns the SCR 160 on sooner. When
the SCR 160 turns on sooner in each half cycle, the effective voltage of
the motor 12 is higher and, therefore the motor 12 speed is
correspondingly higher. As the trigger 50 moves rearwardly toward the end
of its stroke, wiper 68 connects rivet contact 88 via a PC path 48 to the
terminal 176 which shunts, or bypasses, the anode 158 and cathode 178 of
the SCR 160. This connects the motor 12 to full A.C. line voltage and
places the motor 12 into high speed operation. Of course, as the trigger
50 is released from the full "on" position, the above described operations
are reversed in order of occurrence and the motor 12 speed decreases to
zero at the full "off" position.
The reversing switch 112 is a DPDT PC switch which, when actuated, reverses
the armature 13 terminals of the motor 12 relative to the field 164 which
always remains connected in the same direction relative to the line
voltage terminals 174 and 176. The armature 13 is connected to the common
center terminals 166 and 170 and suitable PC conductor paths 48. A
crossing pattern consisting of a PC conductor path 48 and a jumper wire or
path (48) located on the underside of the body of the switch 112 connects
the outside switching terminals of the switch and allows reversing to take
place. It should be noted that the connected positions of the armature 13
and the field 164 can be interchanged, reversed the field relative to the
armature with no change in performance and achieving proper motor
reversal.
The RC module 83 contains a secondary resistor 186 in series with the main
variable resistor 82. By trimming the secondary resistance 186, the
initial speed of the motor, when it is first turned on, can be adjusted
for the desired slow or "creep speed". Trimming can be accomplished with a
laser or other suitable means of increasing the resistance by removing
material from the secondary resistor 186.
The use of a single spring 138 for double duty of both trigger and
lock-release action simplifies the components and assembly procedures. The
spring 138 is conveniently nested in the recess 62 intermediate the
trigger 50 and lock-release member 130. Thus spring hang-up is minimized
and quick, positive spring response is assured for both trigger release
and lock-release member release.
It will be understood that various changes in the details, materials,
arrangements of parts and operating conditions which have been herein
described and illustrated in order to explain the nature of the invention
may be made by those skilled in the art within the principles and scope of
the invention.
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