U.S. patent number 3,881,081 [Application Number 05/422,597] was granted by the patent office on 1975-04-29 for trigger mechanism for a power tool.
This patent grant is currently assigned to Robert Bosch G.m.b.H.. Invention is credited to Ladislaus Ferenczefy, Rainer Schilling.
United States Patent |
3,881,081 |
Schilling , et al. |
April 29, 1975 |
Trigger mechanism for a power tool
Abstract
An electromotor-driven power tool has a trigger mechanism
controlling the operation of the electromotor. The trigger
mechanism comprises a trigger constructed as an one-arm lever
pivotable between an inactive and an active position in which
latter it activates a switch controlling the supply of electric
power to the electromotor. A latch member is supported in the
trigger so as to be movable with respect thereto from a latching
position in which it prevents the trigger from being displaced, to
an intermediate position in which it permits displacement of the
trigger into the active position thereof and its immediate return
into the inactive position once a pressure exerted on the trigger
is relieved, and beyond the intermediate position to a locking
position in which the trigger is retained in the active position
until the latch member is released either by deliberate action of
the operator or by an impact.
Inventors: |
Schilling; Rainer (Stuttgart,
DT), Ferenczefy; Ladislaus (Leinfelden,
DT) |
Assignee: |
Robert Bosch G.m.b.H.
(Stuttgart, DT)
|
Family
ID: |
5876412 |
Appl.
No.: |
05/422,597 |
Filed: |
December 12, 1973 |
Foreign Application Priority Data
|
|
|
|
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Mar 30, 1973 [DT] |
|
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2315841 |
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Current U.S.
Class: |
200/522;
200/318.1; 200/321 |
Current CPC
Class: |
H01H
9/06 (20130101); F16P 3/00 (20130101); H01H
3/20 (20130101) |
Current International
Class: |
F16P
3/00 (20060101); H01H 9/02 (20060101); H01H
9/06 (20060101); H01H 3/20 (20060101); H01H
3/02 (20060101); H01h 003/20 () |
Field of
Search: |
;200/321,322,157,60,323,324,325 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Schaefer; Robert K.
Assistant Examiner: Smith; William J.
Attorney, Agent or Firm: Striker; Michael S.
Claims
What is claimed as new and desired to be secured by Letters Patent
is set forth in the appended claims:
1. In a power tool having an electrically energizable drive
controlled by a switch and accommodated in a housing, a combination
comprising a trigger connected with the switch and mounted on the
housing for displacement with respect thereto between a
deenergizing position in which the switch is open and an energizing
position in which the switch is closed whereby the drive is
energized; biasing means urging said trigger toward said
deenergizing position; a latch member mounted on said trigger to
share the displacement thereof and also for movement with respect
to said trigger between a first, a second, and a third position;
and means on the housing operative for engaging said latch member
when the same is in said first position so as to prevent
displacement of said trigger toward said energizing position, for
disengaging said latch member when the same is in said second
position so as to permit displacement of said trigger against the
force of said biasing means toward said energizing position, and
for reengaging said latch member when the same is subsequently
moved to said third position while said trigger is in said
energizing position whereby to lock said trigger in said energizing
position.
2. A combination as defined in claim 1, wherein said trigger is an
elongated lever supported in the housing for pivotal movement.
3. A combination as defined in claim 2, wherein said biasing means
is a spring acting on said trigger so as to pivotally displace the
same toward said deenergizing position.
4. A combination as defined in claim 1, said means comprising a
catch affixed to the housing and having a projecting portion; and
wherein said latch member comprises a stop located opposite said
projecting portion when said latch member is in said first
position, and is further provided with a recess adapted to accept
said projecting portion subsequently to the displacement of said
latch member into said second position and of said trigger into
said energizing position.
5. In a power tool having a housing including a handle and an
electrically energizable drive controlled by a switch, a
combination comprising a trigger movable in a first direction
between a first position in which the switch is open and a second
position in which the switch is closed whereby the drive is
energized, said trigger being formed with a guide means comprising
a first and a second abutment; biasing means urging said trigger
toward said first position; a latch member supported by said guide
means of said trigger for movement with respect thereto in a second
direction substantially normal to said first direction between a
latch position in which said latch member prevents said trigger
from being displaced, a working position in which said latch member
registers with said first abutment and permits displacement of said
trigger into said second position in response to a pressure exerted
upon said trigger, and permits the return of said trigger into said
first position under the urging of said biasing means subsequently
to relief of the pressure upon said trigger, and a locking position
in which the latch member registers with said second abutment and
subsequently to the displacement of said trigger in said second
position; and means for retaining said trigger in said second
position while said latch is in said locking position.
6. In a power tool having a housing including a handle and an
electrically energizable drive controlled by a switch, a
combination comprising a trigger in a first direction between a
first position in which the switch is open and a second position in
which the switch is closed whereby the drive is energized; biasing
means urging said trigger toward said first position; a latch
member supported by said trigger for movement with respect thereto
in a second direction substantially normal to said first direction
and between a latching position in which said latch member prevents
said trigger from being displaced, a working position in which said
latch member permits displacement of said trigger into said second
position in response to a pressure exerted upon said trigger, and
permits the return of said trigger into said first position under
the urging of said biasing means subsequently to relief of the
pressure upon said trigger; and additional biasing means urging
said latch member toward said latching position thereof.
7. A combination as defined in claim 6, wherein said biasing means
is a spring accommodated in said latch member and abutting against
a portion of said trigger.
8. A combination as defined in claim 7, comprising an additional
spring attached to said portion of said trigger and abutting
against said latch member subsequently to movement thereof beyond
said working position toward said locking position.
9. In a power tool having a housing including a handle and an
electrically energizable drive controlled by a switch, a
combination comprising a trigger formed as an elongated lever
supported in the handle of the power tool for pivotal movement in a
first direction between a first position in which the switch is
open and a second position in which the switch is closed whereby
the drive is energized; biasing means urging said trigger toward
said first position; a latch member supported by said trigger for
movement with respect thereto in a second direction substantially
normal to said first direction and substantially coinciding with
the longitudinal direction of said trigger between a latching
position in which said latch member prevents said trigger from
being displaced, a working position in which siad latch member
permits displacement of said trigger into said second position in
response to a pressure exerted upon said trigger, and permits the
return of said trigger into said first position under the urging of
said biasing means subsequently to relief of the pressure upon said
trigger and a locking position subsequently to the displacement of
said trigger into said second position; and means for retaining
said trigger in said second position while said latch member is in
said locking position, and comprising a catch affixed to the handle
of the power tool and having a projecting portion, and a projection
provided on said latch member and engaging said projecting portion
when said latch member is in said locking position.
10. A combination as defined in claim 9, further comprising
additional biasing means urging said latch member toward said
working position and said latching position; and wherein the
engagement between said projection of said latch member and said
projecting portion of said catch is due to a friction force between
the former and the latter, said friction force exceeding a biasing
force exerted by said additional biasing means.
11. A combination as defined in claim 10, wherein said projecting
portion is provided with an angular end portion, said latch member
is provided with a recess adapted to accommodate said projecting
portion subsequently to displacement of said latch member into said
working position and of said trigger into said second position and
between said working position and said locking position of said
latching member; and wherein said projection extends into said
recess so as to engage said angular end portion of said catch.
12. A combination as defined in claim 11, wherein said catch is an
angular strip member.
Description
BACKGROUND OF THE INVENTION
The present invention relates to power tools in general, and to
electromotor-driven power tools in particular. Even more
particularly, the present invention relates to a trigger mechanism
for use in an electromotor-driven power tool.
There are already known various electromotor-driven power tools
which are provided with trigger mechanisms controlling the supply
of electric current to the electromotor. In most cases, such
trigger mechanisms are arranged within or adjacent the handle of
the power tool so as to enable the operator of the device to
control the trigger mechanism while grasping the handle of the
power tool. There are also already known various trigger mechanisms
which permit a selection of the mode of operation of the power
tool, having two settings, in one of which the power tool is
operative only as long as the operator holds the trigger device,
and in the other one of which the power tool is operative until the
operator releases the trigger device.
There are also already known electromotor-driven power tools in
which the danger of injuries is significantly reduced in that the
trigger mechanism is so constructed as to prevent accidental
putting of the power tool into operation without a willful act on
the part of the user. However, experience has shown that serious
injuries to the user can also occur if a power tool having a
trigger mechanism of the afore-described type is allowed to operate
after the operator has ceased to act on the trigger mechanism
without actually releasing the latter.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an
electromotor-driven power tool having a trigger mechanism of the
abovementioned type which is devoid of the disadvantages of the
prior-art power tools.
More particularly, it is an object of the present invention to
provide a trigger mechanism for such a power tool, whose
utilization reduces the danger of injury to the operator of the
power tool.
It is a further object of the invention to provide a power tool
having a trigger mechanism allowing operation of the power tool in
two settings, the first one of which provides for intermittent
operation as long as the operator depresses the trigger mechanism,
the other one being a locked setting for continuous operation until
the operator releases the trigger mechanism.
It is still another object of the invention to provide a power tool
having a trigger mechanism which activates the electromotor only as
a result of a deliberate action on the part of the operator.
It is yet another object of the invention to provide a power tool
trigger mechanism which becomes released from its locked setting in
response to an impact.
It is an additional object of the present invention to provide a
trigger mechanism for a power tool in which the conversion from
intermittent to continuous setting is a result of deliberate action
on the part of the operator.
In pursuance of these objects and others which will become apparent
hereinafter, one feature of the invention resides in the provision
of a latch member which is supported in a trigger member so as to
be movable substantially transversely to the direction of movement
of the trigger member between a latching position in which it
prevents the trigger member from moving, through an intermediate
position in which it permits the trigger member to move into an
active position so as to activate a switch controlling the supply
of electric current to the electromotor, and into a locking
position in which it retains the trigger member in the active
position thereof. As long as the latch member is in its latching
position, accidental exertion of force on the trigger member does
not result in the displacement with attendant activation of the
switch. Once the latch member is deliberately moved into its
intermediate position, the trigger member is permitted to move in
response to a force exerted upon it by the operator so that the
switch is activated and the electromotor of the power tool operates
as long as the force is being exerted upon the trigger member,
while the trigger member is free to return to its original position
upon discontinuance of the force, with attendant return of the
latch member into its original latching position. Thus, the
intermittent operation of the power tool requires deliberate
displacement of the latch member from its latching position into
its intermediate position and subsequent displacement of the
trigger member. When it is desired to lock the trigger member in
its active position, a further deliberate action on the part of the
operator is required in displacing the latch member even farther
with respect to the trigger member from the intermediate position
into the locking position. Once the latch member is in its locking
position, the pressure on the trigger member may be discontinued
while the trigger member is held in its active position by the
latch member.
Thus, unless the latch member is in its locking position,
discontinuance of pressure on the trigger member results in
deactivation of the switch and thus the electromotor of the power
tool is shut off every time the power tool is laid out of hand,
while any subsequent activation thereof is only possible after the
latch member has been displaced into its intermediate position. As
a result of this arrangement, the danger of injury to the personnel
handling the power tool during the intermittent operation of the
power tool is significantly reduced, and the danger of accidental
starting of the electromotor is prevented.
According to a further feature of the invention, the latch member
is supported in the trigger member for movement transversely of the
direction of movement of the trigger member itself, and the trigger
member is provided with two stepped abutments generally
corresponding to the intermediate and the locking position of the
latch member. Thus, during the intermittent operation of the power
tool, the finger of the operator which exerts pressure on the latch
member so as to displace the same from its latching into its
intermediate position is prevented by the first one of the
abutments from continuing its travel with respect to the trigger
member beyond the position corresponding to the intermediate
position of the latch member, so that accidental locking of the
trigger member in its active position is prevented. When it is
desired to lock the trigger member in its active position, the
operator has to lift at least that finger which contacts the latch
member off the trigger member so as to be able to push the latch
member beyond its intermediate position toward the second abutment
and thus into its locking position. Thus, the conversion from an
intermittent to a continuous operation of the power tool is the
result of a deliberate action of the operator. Consequently, the
danger that the operator may suffer injuries as a result of the
latch member being in the locking position without knowledge about
this fact on part of the operator, is eliminated.
It is a further feature of the present invention that the latch
member is retained in its locking position with a force which is
only sufficient to retain the latch member during the normal
operation of the power tool, while an impact or excessive
vibrations result in return of the latch member into the
intermediate position and from there into the latching position,
provided no force is exerted upon the trigger member. Consequently,
the supply of electric current to the electromotor is discontinued
every time the power tool is subjected to external forces, such as
occur when the power tool is dropped, so that injuries which may be
otherwise suffered by the operator subsequently to his accidentally
dropping the tool are avoided.
The novel features which are considered as characteristic for the
invention are set forth in particular in the appended claims. The
invention itself, however, both as to its construction and its
method of operation, together with additional objects and
advantages thereof, will be best understood from the following
description of specific embodiments when read in connection with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view of a power tool utilizing a
trigger mechanism according to the invention;
FIG. 2 is a detailed, partially sectioned view of the handle of the
power tool according to FIG. 1 showing the trigger mechanism;
FIG. 3 is a detailed, partly sectioned view of a trigger of the
trigger mechanism; and
FIG. 4 is a detailed, partly sectioned view of a latch member of
the trigger mechanism.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A power tool, which is illustrated in FIG. 1 as a sander but which
is not limited to this particular embodiment, comprises a housing
which, in a known manner, includes a main portion 1 accommodating
an electromotor M, a head 2 connected to the main portion 1 and
accommodating a transmission T for driving a tool, such as a sander
plate 3, and a handle 4 which is shown in more detail in FIG. 2 and
which extends from the main portion 1.
An electric switch 5 of conventional design known per se is
accommodated within the handle 4 and is adapted to control the
supply of electric current to the electromotor M. A trigger 6 which
is constructed as an elongated one-armed lever is attached to the
handle 4 so as to be pivotable in a limited range about a pin 6'. A
further pin 7' connects an actuating rod 7 to the trigger 6, the
rod 7 being accommodated in the switch 5 and adapted to activate
the same. Biasing means, such as a spring 8, is accommodated in a
hole 8' provided in the trigger 6 and abuts against the switch 5 or
a stationary part of the handle 4 so as to bias the trigger 6 away
from the switch 5 into its normal undepressed position with
attendant partial emergence of the actuating rod 7 out of the
switch 5, in which position the switch 5 disconnects the
electromotor M from the power source. FIG. 2 shows the trigger in
its undepressed position.
The free end of the trigger 6 is provided with a guide 9 for
guiding a latch member 10. In a currently preferred embodiment, the
guide 9 comprises two lateral walls each of which is provided with
a guide rail 11. The latch member 10 is provided with a pair of
grooves 12 which are adapted to accommodate the guide rails 11 of
the lateral walls of the guide 9. Once the guide rails 11 are
inserted into the grooves 12, the latch member 10 is supported in
the trigger 6 for displacement with respect thereto in a direction
determined by the orientation of the grooves 12. It is to be
understood that instead of being provided in the latch member 10,
the grooves may also be provided in the guide 9; then, of course,
the latch member 10 is formed with corresponding guide rails.
Advantageously, the grooves 12, and consequently also the guide
rails 11 extend substantially longitudinally of the trigger 6, so
that the latch member 10 is displaceable substantially normally to
the direction of movement of the trigger 6 about the pin 6'. A
support plate 21 is arranged between the lateral walls of the guide
9, and the latch member 10 is provided with a bore 13 which extends
parallel to the grooves 12. Biasing means, such as a spring 14 is
accommodated in the bore 13 and abuts against the plate 21, biasing
the latch member 10 away from the plate 21 toward a latching
position of the latch member 10. The latch member 10 is further
formed with a stop 15 and a recess 18 cooperating with a catch 16
which is fixed with respect to the handle 4, being attached to a
stationary part thereof, such as to the switch 5. The catch 16 is
preferably an angular part made of sheet material and cooperates
with the latch member 10 in such a manner as to prevent inadvertent
displacement of the trigger 6 when the latch member 10 is in its
latching position as shown in the drawing, and thus to prevent
possible injuries to the operator which could otherwise occur if
the trigger 6 were permitted to move and, consequently, to activate
the electromotor M and thus the sanding plate 3 every time the
operator touches the trigger 6.
It may be seen in FIGS. 2 and 3 that the lateral walls of the guide
9 have a stepped configuration, being formed with a first abutment
17 and a second abutment 19, generally corresponding to an
intermediate and a locking position of the latch member 10,
respectively. It may be further seen in FIGS. 2 and 3 that the
latch member 10 further comprises a projection 20 which extends
into the recess 18. The function of these abutments and this
projection will be explained hereafter.
It has been already mentioned that as long as the latch member 20
is in its latching position, the trigger 10 is prevented from being
displaced in a direction resulting in actuation of the switch 5.
When it is desired to start the electromotor M of the power tool,
the operator has to move the latch member 10 from its latching
position into its intermediate position by exerting pressure on the
latch member 10 until the latter is displaced to such an extent as
to register with the first abutment 17. It is evident that once the
finger of the operator abuts against the first abutment 17, it is
prevented from going any further, and so is the latch member 10,
which is now in its intermediate position. It may be seen in the
drawings that once the latch member is displaced into its
intermediate position --in the drawings toward the left-- against
the biasing force of the spring 14 the catch 16, instead of being
opposite the stop 15 is now opposite the recess 18, so that the
trigger 6 is allowed to pivot about the pin 6' against the biasing
force of the spring 8, thus forcing the actuating rod deeper into
the switch 5 with attendant activation of the electromotor M. As
long as the trigger 6 is in its active position, the switch is
closed and the electromotor M drives the sanding plate 3, while the
latch member 10 is prevented from returning into the latching
position, being retained by the catch 16. However, once the
pressure on the trigger 6 is relieved, the spring 8 returns the
trigger into its inactive position so that the catch 16 emerges
from the recess 18 and the biasing force of the spring 14 displaces
the latch member 10 into its latching position. Consequently, each
of the successive operations of the power tool requires separate
and deliberate displacement of the latch member 10 from its
latching position into its intermediate position against the
biasing force of the spring 14, so that inadvertent exertion of
pressure on the trigger 6 alone without first displacing the latch
member 10 does not activate the electromotor M. This is
particularly advantageous if the power tool is used intermittently
and periods intervene during which the power tool is laid aside, in
that the grasping of the handle with attendant touching of the
trigger does not automatically result in activation of the
electromotor M.
Whenever it is desired that the power tool be in operation for
extended periods of time without the need for the operator to exert
pressure on the trigger 6 for the entire duration of this extended
period, the latch element 10 is pushed beyond its intermediate
position into its locking position. To accomplish this, another
deliberate action is required from the operator of the power tool;
namely, he has to lift at least one finger from the trigger 6 so as
to be able to push the latch member 10 beyond its position in which
it registers with the first abutment 17 and toward the second
abutment 19. In order to be able to do this, the latch member 10
has to be displaced into its intermediate position and the trigger
6 has to be displaced into its active position so that the
electromotor is activated and the catch 16 extends into the recess
18. Only after these initial steps have been taken is it possible
to shift the latch member 10 beyond its intermediate position into
the locking position --in FIG. 2 farther to the left--. Once this
is done, the projection 20 faces an angular end portion 16' of the
catch 16 and if the pressure on the trigger is now released while
the latch member is held in the locking position, the projection 20
abuts against the angular end portion 16' of the catch 16 so that
the friction between the projection 20 and the angular end portion
16' of the catch 16 prevents the latch member 10 from returning
into its intermediate position and from there into its latching
position with attendant stoppage of the electromotor M. In a
currently preferred embodiment, an additional spring 14' is
attached to the plate 21 in such a manner that it abuts against the
latch member 10 once the latter is displaced beyond its
intermediate position, so that the biasing force the operator of
the power tool has to overcome when displacing the latch member 10
from the intermediate position toward the locking position thereof
increases significantly when compared with the force which he has
to overcome during the displacement of the latch member 10 from the
latching position into the intermediate position thereof. This is
an additional safeguard purporting to avoid the displacement of the
latch member 10 into its locking position without the operator of
the power tool being aware of this fact. In the currently preferred
embodiment of the invention, the biasing force exerted on the latch
member 10 by the two springs 14 and 14' is so selected as to be
equal to or only slightly smaller than the friction force between
the projection 20 of the latching member 10 and the angular end
portion 16' of the catch 16. Consequently, the catch 16 safely
retains the latch member 10 in its locking position under normal
operating conditions until the operator decides to discontinue the
operation by exerting pressure on the trigger 6 so that the
projection 20 is lifted off the angular end portion 16' of the
catch 16 with attendant elimination of the friction force, so that
the combined action of the springs 14 and 14' shifts the latch
member 10 into its intermediate position from which it is allowed
to return into the latching position once the pressure on the
trigger 6 is relieved. However, under unusual circumstances, such
as when the power tool falls to the ground, the resulting impact,
combined with inertial forces of the stationary and movable parts
of the trigger mechanism, momentarily lifts the projection 20 of
the angular end portion 16' of the catch 16, with attendant return
of the latch member 10 into its intermediate position and from
there into its latching position while the spring 8 forces the
trigger 6 to return into its inactive position thus shutting off
the electromotor M. In this manner, the electromotor M driving the
power tool is disactivated once the power tool gets out of the
control of the operator thereof, so that the danger of damage which
would otherwise exist if the power tool were operating even after
it got out of control is eliminated.
While the invention has been described as incorporated in a power
tool having an intermittent and a continuous setting, it could also
be used in a power tool working only under intermittent conditions;
in this case, the projection 20 could be omitted and the latch
member would be displaceable only between a latching position and a
working position corresponding to the intermediate position as
described above, having still the same advantages as those
previously described when discussing the latching and the
intermediate positions of the latch member 10. It is also possible
to dispose of the second spring 14' so that there is no step-wise
increase in the force the operator has to overcome when pushing the
latch member 10 beyond the intermediate position thereof, without
appreciable decrease in the reliability of the device. Namely,
since the operator has to lift at least one of his fingers off the
trigger 6 in order to be able to push the latch member 10 beyond
the intermediate position and toward the locking position thereof,
this fact alone makes him aware of the situation without need to
further remind him by increasing the spring force. It is also
possible to provide a single spring 14 having two stiffness
coefficients, the lower one being applicable during the movement of
the latch member 10 from the latching into the intermediate
position, and the higher one being applicable during movement
beyond the intermediate position.
It is also possible to provide the angular end portion of the catch
16 with an aperture adapted to accept the projection 20. It is
equally possible, if so desired, to omit the angular end portion
16' of the catch 16 entirely --the catch 16 is then a strip which
has been bent only once-- and to provide a cutout therein which is
adapted to accept a projection of the latch member 10 therein.
It will be understood that each of the elements described above, or
two or more together, may also find a useful application in other
types of constructions differing from the types described
above.
While the invention has been illustrated and described as embodied
in the power tools, it is not intended to be limited to the details
shown, since various modifications and structural changes may be
made without departing in any way from the spirit of the present
invention.
Without further analysis, the foregoing will so fully reveal the
gist of the present invention that others can, by applying current
knowledge readily adapt it for various applications without
omitting features that, from the standpoint of prior art, fairly
constitute essential characteristics of the generic or specific
aspects of this invention and, therefore, such adaptations should
and are intended to be comprehended within the meaning and range of
equivalence of the following claims.
* * * * *