[0001] The present invention falls within the art field of hand-held power tools and relates
to an electric screwdriver-drill intended in particular for the application of internally
threaded hollow inserts. Such inserts are applied, for instance, to sheet metal or
similar flat material of limited thickness in order to provide anchorages for fasteners
such as screws, etc..
[0002] The insert comprises a cylindrical element with a hollow cylindrical bore, of which
one end affords a flange and the remaining end is internally threaded and merges with
a central part of reduced thickness designed to deform radially by upsetting when
force is applied to draw the threaded end back toward the flange.
[0003] As regards tools for the fitment of such inserts, the prior art embraces pneumatic
drivers provided with a dual control by which a bolt, threaded at one end to match
the internal thread of the insert, is screwed into and unscrewed from the cylindrical
element in two distinct steps. More exactly, the bolt is inserted into the bore from
the flanged end and screwed tight so as to draw the threaded end of the cylindrical
element forcibly toward the flange, which remains sandwiched between a locating surface
afforded by the tool and the flat surface of the material to which the insert is fixed;
thereafter, the bolt is unscrewed and removed to vacate the bore and leave the insert
ready for use.
[0004] From the construction standpoint, this type of tool requires a system for verifying
and controlling the degree of torque transmitted to the upsetting bolt that is somewhat
complex in mechanical terms.
[0005] Moreover, the direction of rotation is reversed by the operator essentially in arbitrary
fashion on receipt of an indication, provided by mechanical means, that the insert
is fully upset and secure.
[0006] Needless to say, it is difficult to use equipment of the type in question with any
appreciable degree of precision and automatic control.
[0007] The object of the present invention is to provide a hand-held screwdriver-drill in
which the direction of rotation can be reversed automatically to remove the upsetting
bolt once the screwing operation is complete and the insert is secured in position.
[0008] The stated object is comprehensively realized in a screwdriver-drill as characterized
in the appended claims.
[0009] The invention will now be described in detail, by way of example, with the aid of
the accompanying drawings, in which:
- fig 1 provides a schematic illustration of the screwdriver-drill according to the
invention, with certain parts viewed in section and others omitted better to reveal
others;
- fig 2 is the block diagram of an electronic device forming part of the screwdriver-drill
of fig 1.
[0010] With reference to the drawings, a screwdriver-drill according to the present invention,
denoted 1 in its entirety, is intended in particular for fitting inserts 50 of the
type shown in fig 1, consisting in a hollow cylindrical element 51 that affords a
flange 52 at one end, and an internally threaded stretch 53 at the other end. The
flange 52 and the threaded end 53 are interconnected by a central section 54 of reduced
thickness which is designed to upset, spreading in the radial direction, when a contracting
force is applied the insert 50 in such a way as to draw the threaded end 53 toward
the flanged end 52. Applied to an insert 50 occupying a hole 32 in a panel of sheet
metal 33, for example, this contracting force has the effect of tightening the cylindrical
element 51 against the panel 33 on the side opposite from the flange 52.
[0011] The drill 1 is conventional in basic embodiment, comprising a case 4 that houses
and supports a power mechanism including an electric motor 2 and a prismatic shank
or spindle 3 for the connection of attachments or chucking devices (not illustrated).
[0012] The case 4 affords an integrally moulded hand grip enabling an operator to lay hold
on the tool, and an on-off switch 5 controlling the electrical power supply line 6
to the electric motor 2.
[0013] The drill 1 according to the invention comprises an interchangeable upsetting bolt
7 of which one end 8 is threaded to match the internally threaded end 53 of the insert
50 and the opposite end 9 is embodied as a shank coupled positively and coaxially
to the prismatic spindle 3.
[0014] 11 denotes retaining and support means associated with and removable from the case
4, which serve both as a depth gauge designed to locate against the flange 52 of the
insert 50, and as a means of disallowing axial movement of the bolt 7 relative to
the flange 52 when the bolt 7 is introduced into the insert 50 from the flanged end,
engaged with the internally threaded end 53 of the cylindrical element 51 and set
in rotation by the prismatic spindle 3 to apply the upsetting force.
[0015] The drill 1 further comprises an electronic unit 10 for monitoring and controlling
the operation of the electric motor 2, connected to the electrical power supply line
6 between the on-off switch 5 and the motor 2; the unit 10 in question comprises at
least one voltage regulator 12 wired on the input side to the switch 5, hence to the
power supply 6, and able to generate output voltage of a predetermined value that
is a function of the maximum rated torque of the motor 2. The output of the voltage
regulator 12 is connected to the input of an absorbed current transducer 13, the output
of which is a continuous voltage proportional to the current absorbed by the motor
2; this is used to pilot a device 14 capable of inverting the polarity of the power
supply to the electric motor 2, hence reversing its direction of rotation, whenever
the current input to the transducer 13 becomes equal to or greater than a predetermined
value corresponding, in practice, to the current absorbed by the motor 2 in developing
a degree of power such as will torque the spindle 3 sufficiently to clinch the insert
50, drawing the threaded end 53 further toward the flange 52 at the moment in which
the central section 54 has been fully upset by the action of the bolt 7 and thus securing
it to best possible effect.
[0016] The voltage regulator 12 and the absorbed current transducer 13 are interlocked to
means 15 by which to control the value of the input voltage to the inverter 14; these
same means 15 also control the maximum absorbed current value, determined on the basis
of the mechanical deformation properties of the insert 50, which triggers the activation
of the inverter 14.
[0017] Such control means 15 might consist in a regulator calibrated in discrete steps,
with a continuous regulator to give fine adjustment.
[0018] The output from the absorbed current transducer 13 to the inverter 14 is taken off
additionally to an electronic monitoring and control loop 16 capable of limiting the
threshold current values beyond which the inverter is triggered into operation.
[0019] The monitoring and control loop 16 comprises a filter 17 serving to eliminate mains
interference and limit the peak voltage at the output of the absorbed current transducer
13 when the motor 2 is started up, a threshold circuit 18 of which the output signal
is dependent on a predetermined input value, and a corrective delay network 19 serving
both to effect an additional filtering action in respect of the voltage signal from
the absorbed current transducer 13 by eliminating the residual peak value when the
motor is started, and to delay the activation of the inverter 14 for a selectable
interval sufficient, in practical terms, to ensure that the insert 50 is fully upset
and clinched.
[0020] Such a delay is indispensable should it happen, as the insert 50 begins to deform,
that greater power is required from the electric motor 2 in order to generate a torque
capable of overcoming resistance offered by a particularly rigid or tough insert 50;
higher power in turn dictates proportionally higher values of absorbed current, and
earlier activation of the inverter device 14 by the transducer 13.
[0021] Accordingly, in this instance, the corrective delay network 19 will retard the inversion
signal for a duration sufficient to allow the motor 2 to clinch the insert 50 fully.
[0022] The corrective network 19 is adjustable, in that its delay time constant in respect
of the input signal can be increased or decreased.
[0023] The output of the corrective network 19 is directed into a memory circuit 20 by which
the correction signal is retained so as to avoid any unwarranted interruption of the
inversion signal, and emission of a further inversion signal, in the event of a momentary
break in the power supply 6 occasioned by accidental release of the switch 5, for
example.
[0024] The inverter 14 is also wired direct to the power supply input 6 by way of an auxiliary
circuit 6a and activated at the moment when this same circuit is activated.
[0025] The threshold circuit 18 is interlocked likewise to the control means 15, and its
threshold value thus regulated according to the mechanical deformation properties
of the insert 50.
[0026] The inverter 14 is connected further to means 14a for reversing the direction of
rotation manually.
[0027] The memory circuit 20 is interlocked to a relative reset/reset-delay circuit 21 wired
directly in its turn to the on-off switch 5, by means of which the memory reset can
be retarded. This is of particular importance in preventing parasitic oscillations
or unwanted reverse manoeuvres; in effect, time must be allowed for the motor 2 to
stand still before a further cycle can be commenced in order to avoid inversions of
rotation with the motor still in movement, and the electrotechnical problems that
would ensue from such an event.
[0028] Reverting now to the mechanical features of the screwdriver-drill according to the
invention, the upsetting bolt 7 (fig 1) exhibits an intermediate boss, denoted 7g,
whilst the shank end 9 coupled with the prismatic spindle 3 affords a socket 23 matched
to and accommodating the profile of the spindle 3. In the preferred embodiment of
fig 1, this end 9 of the bolt 7 is fashioned in two parts: a prismatic shank 9t integral
with the bolt 7, and a sleeve 31 which positively ensheaths both the prismatic spindle
3 and the prismatic shank 9t of the bolt 7.
[0029] The retaining and support means 11 consist in an axially hollow shroud 24, an interchangeable
stop collar 27, and a locking cap 28.
[0030] The shroud 24, which can be fastened to and removed from the case 4, freely encompasses
the end 9 of the bolt 7 associated with the prismatic spindle 3 and affords a seating
25 in which to accommodate dynamic restraint means 26 breasted frontally with the
boss 7g of the bolt 7 and serving to keep the shank 9 stably in association with the
spindle 3.
[0031] The stop collar 27 can be fastened to and removed from the shroud 24, and is designed
to register with the flange 52 of the insert 50; when fitted, the collar is disallowed
angular movement about the axis of rotation of the spindle 3. To advantage, a screw
fit between the cap 28 and the shroud 24 permits of securing the collar 27 and allows
its removal and replacement according to the external diameter of the insert 50, thereby
achieving the interchangeability aforementioned.
[0032] The shroud 24 is embodied in two coaxial parts 29 and 30, the first 29 fastened permanently
to the case 4 and the second 30 associated with the first by fitment of the locking
cap 28; accordingly, the second part 30 can be made interchangeable to suit the external
diameter of the insert 50. The two parts 29 and 30 of the shroud 24 thus provide the
seating 25 for the dynamic restraint means 26, which can take the form of conventional
thrust bearings.
[0033] It will be clear enough that a drill structured in the manner described above can
be utilized to fit different sizes of inserts 50 simply by changing the upsetting
bolt 7, the stop collar 27 and the removable part 30 of the shroud 24 together with
the thrust bearing, and effecting the appropriate adjustment of the current transducer
13 and the threshold circuit 18.
[0034] In a screwdriver-drill according to the invention, the drawbacks stated at the outset
are overcome by expedients affording simplicity, precision and compactness, and in
particular, enabling the use of a reliable electric motor with limited servicing requirements.
[0035] Moreover, the precision of the control afforded is notable.
1) A screwdriver-drill (1), comprising a case (4) espectively housing and supporting
an electric motor (2) and a prismatic spindle (3) to which attachments or chucking
devices can be connected, and incorporating an on-off switch (5) wired into the electrical
supply line (2) to the motor (2), intended in particular for applying inserts (50)
of the type consisting in a hollow cylindrical element (51) affording a flange (52)
at one end and an internal thread at the opposite end (53) merging with a central
section (54) of reduced thickness that is designed to upset by spreading radially
when a contracting force is applied to draw the threaded end (53) toward the flange
(52), characterized
in that it comprises:
- an interchangeable upsetting bolt (7) of which one end (8) is threaded to match
the threaded end (53) of the insert (50) and the remaining end is coupled coaxially
to the prismatic spindle (3);
- retaining and support means (11) associated with and removable from the case (4),
serving to provide a locating element offered to the flanged end (52) of the insert
(50) and to disallow axial movement of the upsetting bolt (7) in relation to the flange
when the bolt (7) is introduced into the axial bore of the insert (50) by way of the
flanged end (52), screwed into the threaded end (53) of the insert and set in rotation
by the prismatic spindle (3) to apply the contracting force;
- an electronic unit (10) monitoring and controlling the operation of the electric
motor (2), wired into the electrical power supply line (6) between the on-off switch
(5) and the motor and comprising: at least one voltage regulator (12) connected on
the input side to the part of the power supply line (6) controlled by the on-off switch
(5) and delivering an output voltage of predetermined value that is a function of
the maximum torque developed by the motor; an absorbed current transducer (13) driven
by the voltage regulator (12), of which the output is a continuous voltage proportional
to the current absorbed by the motor; and a device (14), piloted by the absorbed current
transducer (13) and capable of inverting the polarity of the electrical power supply
to the electric motor (2) hence of reversing its direction of rotation, at the moment
in which the transducer (13) senses a current value equal to or greater than the value
of the current absorbed by the motor (2) in developing power sufficient to produce
torque at the prismatic spindle (3) such as will draw the threaded end (53) of the
insert (50) closer to the flange (52) once the central section (54) of the insert
has been fully upset by the action of the bolt (7), and thus secure the insert to
best possible effect.
2) A screwdriver-drill as in claim 1, wherein the voltage regulator (12) and the absorbed
current transducer (13) are interlocked to means (15) by which to control the values
of the output voltage supplied to the inverter device (14) and of the absorbed current
limit that triggers activation of the inverter device (14), respectively, according
to the mechanical deformation properties of the insert (50).
3) A screwdriver-drill as in claim 1, wherein the output signal directed from the absorbed
current transducer (13) into the inverter device (14) is taken off additionally to
an electronic monitoring and control loop (16) capable of limiting the threshold values
of absorbed current beyond which the activation of the inverter device (14) is triggered.
4) A screwdriver-drill as in claim 3, wherein the monitoring and control loop (16) comprises,
in sequence:
- a filter (17), connected to the absorbed current transducer (13), capable of eliminating
mains interference and limiting the voltage peak which registers at the output of
the absorbed current transducer (13) when the motor (2) is started;
- a threshold circuit (18) capable of generating an output signal dependent upon a
given input signal value;
- a corrective delay network (19) designed to eliminate residual peak starting voltage
and able to retard the activation of the inverter device (14) for a selectable duration
sufficient to ensure that the insert (50) is fully upset and secured;
- a memory circuit (20) by which the signal from the corrective network (19) is retained
to the end of avoiding any interruption of the inversion signal, and emission of a
further inversion signal, caused as the result of a momentary break in the power supply
line (6).
5) A screwdriver-drill as in claim 1, wherein the inverter device (14) is also connected
directly to the power supply line (6) by way of an auxiliary circuit (6a) and activated
at the moment of activating the circuit.
6) A screwdriver-drill as in claim 4, wherein the voltage regulator (12), the absorbed
current transducer (13) and the threshold circuit (18) are interlocked to means (15)
by which to control the values of the voltage supplied to the inverter device (14),
of the absorbed current limit which triggers activation of the inverter device (14)
and of the maximum threshold, respectively, according to the mechanical deformation
properties of the insert (50).
7) A screwdriver-drill as in claim 1, wherein the inverter device (14) is connected
to means (14a) by which inversion can be controlled manually.
8) A screwdriver-drill as in claim 4, wherein the memory circuit (20) is interlocked
to a relative reset/reset-delay circuit (21) connected directly to the on-off switch
(5) and capable of delaying reset of the memory.
9) A screwdriver-drill as in claim 1, comprising an upsetting bolt (7) embodied with
an intermediate boss (7g), and a socket (23) at the end (9) coupled coaxially with
the prismatic spindle (3) by which the spindle (3) is accommodated in its entirety,
wherein retaining and support means (11) comprise:
- an axially hollow shroud (24) freely accommodating the end (8) of the upsetting
bolt (7) coupled with the prismatic spindle (3), associated removably with the case
(4) and affording a seating (25) to accommodate dynamic restraint means (26) by which
the bolt (7) is kept in positive association with the prismatic spindle (3);
- a stop collar (27) designed to register against the flange (52) of the insert (50),
associated with the shroud (24) removably and in such a way as to remain incapable
of angular movement about the axis of rotation of the prismatic spindle (3) when in
use;
- a locking cap (28) serving to secure the stop collar (27) to the shroud (24), and
removable to permit of replacing the collar (27) according to the external diameter
of a given insert (50).
10) A screwdriver-drill as in claim 9, wherein the shroud (24) is embodied in two coaxial
parts, of which a first part (29) is associated permanently with the case (4) and
a second part (30) is secured to and removable from the first by means of the locking
cap (28) in such a way as to be rendered interchangeable in respect of the external
diameter of the insert (50), and of which the encompassed space affords the seating
(25) for the dynamic restraint means (26).
11) A screwdriver-drill as in claim 9, wherein the end (9) of the upsetting bolt (7)
coupled with the prismatic spindle (3) is embodied in two parts, consisting in a prismatic
shank (9t) integral with the bolt and an axial sleeve (31) by which both the prismatic
spindle (3) and the prismatic shank (9t) are positively ensheathed.