U.S. patent application number 13/142696 was filed with the patent office on 2012-02-23 for handheld electric machine tool.
Invention is credited to Stefano Delfini, Thilo Koeder, Joachim Platzer, Jochen Roser, Ivan Spremo.
Application Number | 20120045976 13/142696 |
Document ID | / |
Family ID | 42234752 |
Filed Date | 2012-02-23 |
United States Patent
Application |
20120045976 |
Kind Code |
A1 |
Roser; Jochen ; et
al. |
February 23, 2012 |
HANDHELD ELECTRIC MACHINE TOOL
Abstract
A handheld electric machine tool is described including a
housing with a grip area, a tool area for a tool that is drivable
in a linear and/or oscillating manner, an operating part on the
housing for activation of the tool and/or the electric machine tool
by the user, a drive unit disposed in the housing for producing a
working motion of the tool, an electronic unit disposed in the
housing for acting upon the drive unit with at least control and/or
regulating signals, an operating voltage unit for supplying an
electrical DC voltage, the drive unit including at least one
excitation actuator having a volume of excitation-active material,
which excitation actuator when in operation is electrically
supplied by the operating voltage unit, is controlled or regulated
by the electronic unit. The electronic unit may be configured to
operate the at least one excitation actuator in a resonant
frequency.
Inventors: |
Roser; Jochen; (Ludwigsburg,
DE) ; Delfini; Stefano; (Bettlach, CH) ;
Koeder; Thilo; (Gerlingen, DE) ; Platzer;
Joachim; (Remseck-Hochberg, DE) ; Spremo; Ivan;
(Stuttgart, DE) |
Family ID: |
42234752 |
Appl. No.: |
13/142696 |
Filed: |
December 17, 2009 |
PCT Filed: |
December 17, 2009 |
PCT NO: |
PCT/EP09/67375 |
371 Date: |
October 7, 2011 |
Current U.S.
Class: |
451/358 ;
173/2 |
Current CPC
Class: |
B24B 23/00 20130101;
B24B 1/04 20130101 |
Class at
Publication: |
451/358 ;
173/2 |
International
Class: |
B24B 23/00 20060101
B24B023/00; B24B 49/10 20060101 B24B049/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 5, 2009 |
DE |
102009000030.5 |
Jul 14, 2009 |
DE |
102009027688.2 |
Claims
1-28. (canceled)
29. A handheld electric machine tool, comprising: a housing with a
grip area; a tool area for a tool that is drivable in at least one
of a linear and oscillating manner; an operating part on the
housing for activation by a user of at least one of the tool and
the electric machine tool; a drive unit disposed in the housing to
produce a working motion of the tool; an electronic unit disposed
in the housing to act upon the drive unit with at least one of
control signals and regulating signals; and an operating voltage
unit to supply an electrical DC voltage, wherein the drive unit
includes at least one excitation actuator having a volume of
excitation-active material, which excitation actuator when in
operation is electrically supplied by the operating voltage unit,
is controlled or regulated by the electronic unit; wherein the
electronic unit is configured to operate the at least one
excitation actuator in a resonant frequency.
30. The handheld electric machine tool as recited in claim 29,
wherein the electronic unit includes a regulating unit with
frequency matching for re adjustment of the resonant frequency of
the at least one excitation actuator.
31. The handheld electric machine tool as recited in claim 29,
wherein the excitation-active material is piezoelectric.
32. The handheld electric machine tool as recited in claim 31,
wherein a volume of the piezoelectric material is at least 0.2
cm.sup.3.
33. The handheld electric machine tool as recited in claim 31
wherein a volume of the piezoelectric material is at least 0.5
cm.sup.3.
34. The handheld electric machine tool as recited in claim 31
wherein a volume of the piezoelectric material is at least 1
cm.sup.3.
35. The handheld electric machine tool as recited in claim 32,
wherein the at least one excitation actuator has a power density of
at least 5 Watt/cm.sup.3, based on the volume of the
piezoelectrically active material of the at least one excitation
actuator.
36. The handheld electric machine tool as recited in claim 35
wherein the power density is at least 20 Watt/cm.sup.3.
37. The handheld electric machine tool as recited in claim 29,
wherein the at least one excitation actuator has, at a tip of the
tool, an oscillation amplitude of at least 3 .mu.m.
38. The handheld electric machine tool as recited in claim 37,
wherein the oscillation amplitude is at least 8 .mu.m.
39. The handheld electric machine tool as recited in claim 37,
wherein the oscillation amplitude is at least 12 .mu.m.
40. The handheld electric machine tool as recited in claim 29,
wherein on an input side of the electronic unit, an electrical
power for acting upon the at least one excitation actuator is at
least 20 Watt.
41. The handheld electric machine tool as recited in claim 29,
wherein a disc thickness of the excitation actuator is from 1 mm to
10 mm.
42. The handheld electric machine tool as recited in claim 41,
wherein the disc thickness is between 2 mm to 6 mm.
43. The handheld electric machine tool as recited in claim 41,
wherein the disc thickness is 5 mm.
44. The handheld electric machine tool as recited in claim 31,
wherein an input field strength of the at least one excitation
actuator is in the range below 300 V/mm, based on a thickness of
the piezoelectrically active material.
45. The handheld electric machine tool as recited in claim 44,
wherein the range is from 50 V/mm to 220 V/mm.
46. The handheld electric machine tool as recited in claim 29,
wherein an input voltage of the at least one excitation actuator is
in a range below 1000 Volts.
47. The handheld electric machine tool as recited in claim 46,
wherein the range is from 300 Volts to 700 Volts.
48. The handheld electric machine tool as recited in claim 29,
wherein an electrical output voltage of the operating voltage unit
is below 100 Volts.
49. The handheld electric machine tool as recited in claim 29,
wherein an electrical output voltage of the operating voltage unit
is above 100 Volts.
50. The handheld electric machine tool as recited in claim 29,
wherein an operating frequency of the at least one excitation
actuator is in the range of from 10 kHz to 1000 kHz.
51. The handheld electric machine tool as recited in claim 50,
wherein the range is from 30 kHz to 50 kHz.
52. The handheld electric machine tool as recited in claim 50,
wherein the range is from 35 kHz to 45 kHz.
53. The handheld electric machine tool as recited in claim 29,
wherein the operating voltage unit includes an electrochemical
storage device.
54. The handheld electric machine tool as recited in claim 53,
wherein the electrochemical storage device is rechargeable.
55. The handheld electric machine tool as recited in claim 29,
wherein the operating voltage unit includes a rectifier.
56. The handheld electric machine tool as recited in claim 29,
wherein the electronic unit is concentrated on a printed circuit
board.
57. The handheld electric machine tool as recited in claim 29,
wherein the electronic unit includes at least one inductance
provided in a power circuit acting upon the at least one excitation
actuator with electrical power for at least one of signal filtering
and inductive compensation of the at least one excitation
actuator.
58. The handheld electric machine tool as recited in claim 29,
wherein at least the drive unit, the electronic unit and the
operating voltage unit are distributed in the housing in such a
manner that a center of gravity lies in a region of the grip
part.
59. The handheld electric machine tool as recited in claim 29,
wherein the drive unit further includes at least one further drive
component.
60. The handheld electric machine tool as recited in claim 29,
wherein the at least one excitation actuator forms a main energy
consumer of the electric machine tool, for which at least 50% of
the electrical input power is provided.
61. The handheld electric machine tool as recited in claim 29,
further comprising: at least one of an optical, acoustic, and
haptic operating indicator to indicate an activated state of the at
least one excitation actuator.
62. The handheld electric machine tool as recited in claim 29,
further comprising: an illumination element for a working area.
63. The handheld electric machine tool as recited in claim 29,
wherein the excitation actuator is configured to generate
superimposed oscillations in the tool which are superimposed on a
working motion of the tool.
64. The handheld electric machine tool as recited in claim 29,
wherein the tool is rotatably supported and a working motion of the
tool is a rotational motion.
65. The handheld electric machine tool as recited in claim 64,
wherein the tool is a grinding wheel.
66. The handheld electric machine tool as recited in claim 63,
wherein the superimposed oscillations excite the tool in at least
one of (i) orthogonally to a plane of motion of the tool in which
the working motion of the tool takes place, (ii) in a direction of
the longitudinal axis of a tool shaft carrying the tool, (iii) in a
plane of motion in which the working motion of the tool takes
place, and (iv) perpendicularly to the tool shaft.
67. The handheld electric machine tool as recited in claim 29,
wherein the excitation actuator acts upon a bearing of the
tool.
68. The handheld electric machine tool as recited in claim 29,
wherein an excitation-active material of the excitation actuator is
magneto-restrictive.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a handheld electric machine
tool including a housing with a grip area, a tool area for a tool
that is drivable in a linear and/or rotary oscillating manner, an
operating part on the housing for activation of the tool and/or the
electric machine tool by the user, a drive unit disposed in the
housing for producing a working motion of the tool, an electronic
unit disposed in the housing for acting upon the drive unit with
the required machining output consisting of at least control and/or
regulating signals, an operating voltage unit for supplying an
electrical DC voltage to the electronic unit, the drive unit
including at least one excitation actuator having a volume of
excitation-active material, which excitation actuator when in
operation is electrically supplied by the operating voltage unit
and is controlled or regulated by the electronic unit.
BACKGROUND INFORMATION
[0002] Handheld electric machine tools are characterized by being
portable and by being held and guided by a user by hand when in
operation. They may be cordlessly operated by battery packs or may
be operated with mains current. In particular, they generally
consist of only one housing which is completely held by the
user.
[0003] European Patent No. EP 1 598 171 B1 describes a mechanical
configuration of a welding head of a portable welding gun in which
an ultrasound actuator acts upon the welding head with mechanical
power.
SUMMARY
[0004] The present invention relates to a handheld electric machine
tool including a housing with a grip area, a tool area for a tool
that is drivable in a linear and/or rotary oscillating manner, an
operating part on the housing for activation of the tool and/or the
electric machine tool by the user, a drive unit disposed in the
housing for producing a working motion of the tool, an electronic
unit disposed in the housing for acting upon the drive unit with
the required machining output consisting of at least control and/or
regulating signals, an operating voltage unit for supplying an
electrical DC voltage to the electronic unit, the drive unit
including at least one excitation actuator having a volume of
excitation-active material, which excitation actuator when in
operation is electrically supplied by the operating voltage unit
and is controlled or regulated by the electronic unit.
[0005] The electronic unit is configured to operate the at least
one excitation actuator in a resonant frequency.
[0006] If the excitation actuator is operated with its resonant
frequency, it is possible, with a sufficiently high Q factor of the
oscillating system, for a high mechanical output power to be
delivered corresponding to an electrical input power. The
excitation actuator may be an ultrasound excitation generator,
especially a piezo actuator in the style of a Langevin oscillator.
The piezo actuator has excitation-active material as the
piezoelectric material. Typically, the Q factor of the undamped
oscillating system lies at values above 100, typically above 500.
The resonance system of the excitation actuator, which has the
resonant frequency, includes the Langevin oscillator with
piezoelectrically active material, and components coupled to the
oscillator, especially components that amplify the ultrasound
and/or transmit it to a machining site. Such components are known,
for example, as boosters or sonotrodes. This makes possible a
reduction in overall size and makes it possible to provide a
compact device. That advantageously produces a compact,
high-performance electric machine tool which is handy at the same
time.
[0007] It is also possible for a plurality of excitation actuators,
for example of the same or also of differing resonant frequency, to
be provided as drive components. Alternatively, it is also possible
for one or more further drive components, such as an electric
motor, to be provided. The various drive components may be operated
as alternatives or in combination. If the at least one excitation
actuator is operated in resonance, the power yield is particularly
high, so that, for a given output power of the electric machine
tool, the construction may be particularly compact, which is also
conducive to comfortable handling of the handheld electric machine
tool. The proposed electric machine tool is a one-piece implement
with which it is possible to dispense with troublesome connection
cables between separate housing parts. The electric machine tool
may be operable cordlessly with non-rechargeable or rechargeable
batteries or--in addition or alternatively--may be operable by
mains power via a mains cable. The tool may be an interchangeable
tool detachably connected to the excitation actuator or it may be
fixedly connected to the excitation actuator. The connection may,
for example, be integral or non-positive. The electric machine tool
is especially a machining tool with which objects or surfaces may
be machined or modified, such as, for example, drills, hammer
drills, cutting tools, grinding machines, milling machines, saws,
welding devices and the like.
[0008] In accordance with an advantageous development of the
present invention, the electronic unit may include a regulating
unit with frequency matching for adjustment of the resonant
frequency of the at least one excitation actuator. Advantageously,
during operation of the electric machine tool the resonant
frequency may be continuously adapted if, for example, the resonant
frequency of the excitation actuator changes due to temperature
change, changing of the tool coupled to the excitation actuator or
upon loading of the tool. In that manner, an optimum power yield is
always made possible in operation. Advantageously, the electronic
unit may include a phase-regulating chain with which the resonant
frequency may be excited with high accuracy. In that manner, a
phase shift between the electrical current and electrical voltage
supplied to the piezoelectrically active material to excite the
ultrasonic oscillations may be set and maintained at a fixed value,
especially 0.degree. phase difference between current and voltage
signal, thereby enabling an optimum power yield to be achieved.
[0009] In accordance with an advantageous development of the
present invention, the volume of the piezoelectrically active
material may be at least 0.2 cm.sup.3, preferably 0.5 cm.sup.3,
especially at least 1 cm.sup.3. Advantageously, it is possible for
a sufficient ultrasound power to be achieved with a small overall
size of the excitation actuator.
[0010] In accordance with an advantageous development of the
present invention, the at least one excitation actuator may have a
power density of at least 5 Watt/cm.sup.3, preferably at least 20
Watt/cm.sup.3, based on the volume of the piezo-electrically active
material of the at least one excitation actuator. A correspondingly
high power density is advantageous for a handheld compact electric
machine tool having the smallest possible dimensions and low
production costs.
[0011] In accordance with an advantageous development, the at least
one excitation actuator may have, at the tip of the tool, an
oscillation amplitude of at least 3 .mu.m, preferably at least 8
.mu.m, especially at least 12 .mu.m. A correspondingly high
oscillation amplitude is advantageous for good power transfer to
the workpiece and hence for a high rate of work progress by the
electric machine tool.
[0012] In accordance with an advantageous development of the
present invention, on the input side of the electronic unit an
electrical power for acting upon the at least one excitation
actuator may be at least 20 Watt. Advantageously, it is thereby
possible to ensure sufficient power for an electric machine tool.
Customary power outputs in the do-it-yourself sector are, for small
cutting systems, approximately from 20 Watt to 250 Watt, preferably
from 50 Watt to 150 Watt. For higher-powered applications, for
example drilling, power outputs starting at 50 Watt up to 1000
Watt, preferably from 200 Watt to 500 Watt, are required. In the
professional trade sector, the power requirement for small systems
is approximately from 50 to 400 Watt, preferably from 100 to 250
Watt. In the case of large systems, power outputs of from 200 Watt
to 2000 Watt, preferably from 400 Watt to 1000 Watt, are employed.
It is nevertheless possible to produce an electric machine tool
with handy dimensions which not only is capable of being gripped or
held by the hand of the user but also affords a sufficiently high
power output for machining purposes.
[0013] In accordance with an advantageous development of the
present invention, a maximum electric excitation field strength of
the at least one excitation actuator may be in the range below 300
V/mm (based on the thickness, especially disc thickness, of the
piezoelectrically active material), preferably in the range from 50
V/mm to 220 V/mm. At a disc thickness of the excitation actuator of
typically from 1 mm to 10 mm, preferably from 2 mm to 6 mm, and
especially of around 5 mm, the electrical voltages are below 1000
Volt. That advantageously makes it possible for the excitation
actuator to be used in the handheld electric machine tool with
sufficient mechanical output power while having advantageously
small dimensions.
[0014] In accordance with an advantageous development of the
present invention, an electrical output voltage of the operating
voltage unit when supplied by electrochemical storage devices may
be within from 3 Volt to 100 Volt DC, preferably in the range from
3.5 V to 40 V, and especially may be 36 Volt, 24 Volt, 18 Volt,
14.4 Volt, 12 Volt, 10.6 Volt, 7.2 Volt and 3.6 Volt. It is
advantageously possible to use non-rechargeable battery packs or
rechargeable battery packs that are small and light enough to still
afford easy handling of the electric machine tool at high power
output.
[0015] In accordance with an advantageous development of the
present invention, a DC voltage component of the electrical output
voltage of the operating voltage unit when supplied with mains
voltage may be within from 0.5 U.sub.mains (effective value of
mains voltage) to 2 U.sub.mains. Preferably, for example with the
use of a bridge rectifier with smoothing capacitor, 1.4
U.sub.mains. In a further embodiment, the mains voltage may be
transformed using an input-side transformer to a voltage suitable
for the operating voltage unit.
[0016] In accordance with an advantageous development of the
present invention, the operating frequency of the at least one
excitation actuator may be in the range of from 10 kHz to 1000 kHz,
preferably from 30 kHz to 50 kHz, and especially from 35 kHz to 45
kHz, more especially around 40 kHz. With increasing frequency, the
overall size of the components decreases and the mechanical load on
the oscillating system increases, producing in the selected
frequency range advantageous proportions with high output power and
favorable weight of the electric machine tool.
[0017] In accordance with an advantageous development of the
present invention, the operating voltage unit may include an
electrochemical storage device, preferably a rechargeable
electrochemical storage device. The operating voltage unit takes up
only very little space, which is advantageous in terms of the
compactness and weight of the electric machine tool. Advantageous
systems are those based on, for example, lithium ions (Li ions) or
also nickel-metal hydride (NiMeH), nickel-cadmium (NiCd) or also
lead and the like. These may be fixedly integrated in the housing
and recharged via a charging connection. Alternatively, the
operating voltage unit may be in the form of an exchangeable
system, with replaceable electrochemical storage devices which may
also be rechargeable externally if appropriate and which may be
plugged into a holder provided for the purpose in or on the
housing. Depending on the power output required, the rated voltage
of the operating voltage unit may be, for example, from 3 Volt DC
to 48 Volt DC, for example 12 Volt DC.
[0018] In accordance with an advantageous development of the
present invention, the operating voltage unit may include an AC/DC
transformer unit. In that case, a mains connection may also be
provided for the electric machine tool, and rectification and
smoothing of the mains voltage may take place in the operating
voltage unit. Although the conditioning of the mains voltage
requires more space than an energy storage device, the further
space-saving and compact construction in a single housing still
makes simplified operation and handling of the electric machine
tool possible.
[0019] In accordance with an advantageous development of the
present invention, the electronic unit may be concentrated on a
printed circuit board. That allows a particularly space-saving
arrangement in the housing. The electronic activation system of the
excitation actuator is particularly compact.
[0020] In accordance with an advantageous development of the
present invention, for signal filtering and for inductive
compensation of the at least one excitation actuator at least one
inductance may be provided in a power circuit of the electronic
unit acting upon the at least one excitation actuator with
electrical power. It is possible to achieve a space-saving layout
of the power inductances in a single coil core. The signal
filtering and inductive compensation of the piezo actuator, which
is beneficial in the case of excitation actuators, may be provided
directly by a specifically adjusted stray inductance of a
transmission transformer that is required in any case, or may be
afforded by an inductance wound on the same coil core. An
additional coil core with a further inductance in the power circuit
may thereby be omitted.
[0021] In accordance with an advantageous development of the
present invention, at least drive unit, electronic unit and
operating voltage unit may be distributed in the housing in such a
manner that a center of gravity lies in the region of the grip
part. The user is able to handle the electric machine tool safely
and conveniently. Safety and ease of use are enhanced.
[0022] In accordance with an advantageous development of the
present invention, the drive unit may include, in addition to the
at least one excitation actuator, at least one further drive
component. Advantageously, a motion produced by the at least one
excitation actuator may be superimposed on the working motion of a
tool driven by the at least one further drive component, thereby
enabling work progress to be considerably improved and making the
machining easier.
[0023] In accordance with an advantageous development of the
present invention, the at least one excitation actuator may form a
main energy consumer of the electric machine tool, for which
preferably at least 50% of the electrical input power may be
provided. In an advantageous development, at least 75%, preferably
at least 80%, of the electrical input power may be provided for the
excitation actuator. The rate of work progress of the electric
machine tool when using ultrasound is especially high, and
therefore a further energy consumer, especially a further drive
component, such as a drill, chisel, cutter or the like, may be
smaller. That means that the drive and associated electronic
components and the energy supply may also be smaller, which in turn
allows enhanced ease of use and improved handling of the handheld
electric machine tool.
[0024] In accordance with an advantageous development of the
present invention, one or more operating indicators for an
activated state of the at least one excitation actuator may be
provided. The indicators may be optical and/or acoustic and/or
haptic. The operating safety of the electric machine tool is
increased, since it is clearly evident when the excitation actuator
is activated and capable of delivering mechanical power.
[0025] In accordance with an advantageous development of the
present invention, the drive unit which imparts a working motion to
the tool may impart superimposed oscillations to the tool. The
drive unit may have as a further drive component, for example, an
electric drive motor which is housed in the housing of the electric
machine tool. The motor shaft is normally coupled via a gear unit
to a tool shaft which is the carrier of the tool and executes the
working motion. The tool is usually to be fastened to the tool
shaft in an interchangeable manner.
[0026] The electric machine tool may, for example, be used for
chip-generating machining of workpieces, where, to reduce the chip
size, the excitation actuator, which is able to produce
superimposed oscillations in the tool, is advantageously disposed
in the electric machine tool. Those superimposed oscillations are
superimposed on the working motion of the tool.
[0027] According to the type of electric machine tool and depending
on the tool used and the material of the workpiece to be machined,
the superimposed oscillations, which emanate not from the drive
motor but from the excitation actuator, may be generated with a
frequency that results in a significant reduction in the chip size.
Since smaller chips also have a smaller heat capacity, the chips
are able to cool down in a shorter time, thereby reducing the fire
risk. Furthermore, the smaller chips per se lead to a reduced risk
of injury, since their momentum is lower.
[0028] The frequency of the superimposed oscillations is
expediently in the ultrasound range and may thus be, for example,
at least 20 kHz. That comparatively high frequency has, on the one
hand, the advantage that oscillations in that order of magnitude
are no longer audible to humans, and therefore no noise nuisance
occurs. On the other hand, it has been found that oscillations at
and above that order of magnitude are particularly effective in
significantly reducing the size of the chips produced in the
machining of a workpiece.
[0029] It may be expedient to generate superimposed oscillations
that are in considerably greater orders of magnitude. In principle,
oscillations up to and including the megahertz range come into
consideration. In addition, it is also possible to generate
superimposed oscillations of lower frequency.
[0030] Owing to the superimposition on the working motion of the
tool, on the one hand, and owing to the generally distinctly higher
frequency, the generation of the superimposed oscillations has no
effect on the working motion and hence on the result of the
workpiece machining operation. In addition, the superimposed
oscillations are usually of only a very small amplitude, so that
the machining of the workpiece is not impaired.
[0031] The advantageous generation of superimposed oscillations in
the tool may be used both in rotary and in translational or in a
mixture of rotary and translational working motions of the tool. In
accordance with an advantageous embodiment, the electric machine
tool is in the form of a grinding device, for example an angle
grinder, having as the tool a grinding wheel supported on a tool
shaft, the motion of the tool being exclusively a rotary motion in
that case. There also come into consideration, however,
translational motions, for example in the case of hacksaws which
execute an oscillatory stroke movement.
[0032] The superimposed oscillations may, in accordance with an
advantageous embodiment, be excited orthogonally to the plane of
motion of the tool in which the working motion takes place. For
example, in the case of grinding wheels, the superimposed
oscillations may be applied in the direction of the tool shaft
carrying the grinding wheel. In the case of a translational working
motion, on the other hand, the superimposed oscillation takes place
perpendicularly to the translational motion.
[0033] In accordance with a further advantageous embodiment, it is
also possible, however, for the superimposed oscillations to excite
the tool in the plane of motion. In the case of a grinding wheel,
this means that the grinding wheel is excited perpendicularly to
the tool shaft, so that the vector of the excitation lies in the
plane of motion of the grinding wheel.
[0034] It may furthermore be advantageous to cause the superimposed
oscillations emanating from the excitation actuator to act upon a
bearing of the tool, in which case the oscillations also propagate
via the bearing to the tool. In the case of a plurality of
bearings, this is preferably done via the bearing that is near the
tool in order to avoid loading of the gear unit and the drive motor
by the superimposed oscillations.
[0035] As excitation actuator, it is possible to use active
actuators of various configurations capable of being excited by
supply of energy to generate oscillations. In accordance with an
advantageous embodiment, it may be provided that the excitation
actuator is in the form of a Langevin oscillator, with piezo
elements clamped therein, which changes its dimensions as a result
of application of a voltage. As a result of being acted upon by an
appropriately high-frequency voltage, the piezo element is able to
expand and contract in the desired frequency of the superimposed
oscillations, the excitation actuator being coupled to a component
in the force transmission chain between drive unit or drive motor
and tool so that the oscillations of the excitation actuator may
propagate into the tool. As already described previously, the
excitation is preferably effected by way of a bearing of the tool
shaft carrying the tool. In accordance with an advantageous
embodiment, it is provided that the excitation actuator is in the
form of a magneto-restrictive excitation actuator, which is
especially suitable for generating ultrasonic oscillations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] Further advantages will be apparent from the following
description of the figures. Exemplary embodiments of the present
invention are illustrated in the figures. The figures and the
description contain numerous features in combination. The person
skilled in the art will advantageously also consider the features
individually and combine them to make sensible further
combinations.
[0037] FIG. 1 shows an exemplary embodiment of a handheld electric
machine tool configured as a cutting tool.
[0038] FIG. 2 shows a further exemplary embodiment of a handheld
electric machine tool configured as a drill.
[0039] FIG. 3a, 3b show an outline sketch of an activation assembly
with an AC voltage power supply by mains current or with a DC
voltage power supply by a battery pack (FIG. 3a) and an
advantageous clocking for reducing the overall size of a filter
unit (FIG. 3b).
[0040] FIG. 4 shows a progression of an ultrasound amplitude along
a sonotrode.
[0041] FIG. 5 shows an impedance characteristic for detecting a
resonant frequency of an excitation actuator.
[0042] FIG. 6 shows an equivalent circuit diagram of an ideal
transformer.
[0043] FIG. 7 is a sectional view of an electric machine tool in
the form of an angle grinder.
[0044] FIG. 8 is a detailed view of the grinding wheel of the angle
grinder of FIG. 7, disposed on a tool shaft, the tool shaft being
received in bearings and the bearing near the tool being acted upon
with high-frequency oscillations transversely to the shaft axis by
an excitation actuator.
[0045] FIG. 9 shows the grinding wheel of FIG. 8 with bearing and
excitation actuator in plan view.
[0046] FIG. 10 shows a further exemplary embodiment, in which the
excitation actuator acts upon the tool shaft carrying the grinding
wheel with high-frequency oscillations in the axial longitudinal
direction.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0047] In the Figures, components that are identical or of the same
kind are numbered with identical reference numerals.
[0048] To explain the present invention, FIGS. 1 and 2 show
different examples of handheld electric machine tools 10. FIG. 1
shows a cutting tool with elongate housing shape; FIG. 2 shows a
drill with T-form housing shape.
[0049] Handheld electric machine tool 10 includes a housing 20 with
a grip area 40. A user holds electric machine tool 10 at the grip
area 40 and is able to guide electric machine tool 10. Grip area 40
may, where appropriate, be decoupled from other areas of the
housing by a damping element, not shown. Electric machine tool 10
further includes a tool area 50 for a tool 60 which is drivable in
a linear and/or oscillating manner, for example a cutter (FIG. 1)
or a drill (FIG. 2) or another tool corresponding to another type
of device.
[0050] An operating part 30 on the housing is used for activation
of tool 60 and/or electric machine tool 10 by the user. Operating
part 30 may, for example, be a switch or a controller or may also
include a plurality of operating elements, one of which may be
provided, for example, for switching on electric machine tool 10
and one of which may be provided for switching on and/or
controlling tool 60.
[0051] Arranged in housing 20 there is a drive unit 80 which, in
the examples shown in FIG. 1 and FIG. 2, includes only one drive
component which is formed by an excitation actuator 100. The latter
may be in the form of a piezo-excited Langevin oscillator (also
called a piezo actuator) which includes a volume of
piezoelectrically active material 102, for example piezo-ceramic
discs which are pressed together and which undergo a change in
length when acted upon by electrical voltage. When high-frequency
electrical voltage is applied, in a conventional manner ultrasound
is generated which is passed via a coupling element 106 to a tool
60. Coupling element 106 may be a conventional sonotrode. The
length and shape and also the material of coupling element 106
determine a resonant frequency of excitation actuator 100. Tool 60
may also have an influence on the resonant frequency. In the
embodiment variants in FIG. 1 and FIG. 2, excitation actuator 100
is configured in such a way that Langevin oscillator and coupling
element 106 are combined in a unit, and the total length thereof
approximately corresponds to half the wavelength .lamda./2 of the
ultrasonic oscillation. Other embodiment variants may provide that
excitation actuator 100 is composed of a plurality of components of
length .lamda./2. These may be: oscillation generators, known as
converters, specifically, for example, a Langevin oscillator,
amplitude transformation pieces 104, known as boosters, where
applicable lengthening pieces, and coupling element 106 known as a
sonotrode.
[0052] An electronic unit 200 arranged in housing 20 serves to
apply at least control and/or regulating signals to drive unit 80
and to supply voltage to excitation actuator 100. An operating
voltage unit 90, in the form of a non-rechargeable or rechargeable
battery pack with non-rechargeable or rechargeable batteries 92
here, serves to provide an electrical DC voltage for electronic
unit 90 which converts the operating voltage into a high-frequency
voltage signal with which excitation actuator 100 is excited into
oscillation in the desired manner.
[0053] Electronic unit 200 is configured to operate the at least
one excitation actuator 100 in a resonant frequency f_res.
Electronic unit 200 includes a regulating unit 224 for re
adjustment of the resonant frequency f_res of excitation actuator
100. Regulating unit 224 may include a phase regulating chain
capable of exciting excitation actuator 100 into its resonant
frequency, with a phase shift between incoming current and incoming
voltage being set to 0.degree.. Preferably, resonant frequency
f_res is regulated accordingly if the resonant frequency changes
owing to heating or changing load at the tool. Alternatively,
frequency re-adjustment may also be carried out by regulating to a
maximum of the current fed into excitation actuator 100.
[0054] If excitation actuator 100 is a piezo actuator, the volume
of piezoelectrically active material 102, for example stacked
piezoelectric discs, is advantageously at least 0.2 cm.sup.3,
preferably 0.5 cm.sup.3, especially at least 1 cm.sup.3. Excitation
actuator 100 may have a power density of at least 5 Watt/cm.sup.3,
preferably at least 20 Watt/cm.sup.3, based on the volume of
piezoelectrically active material 102 of excitation actuator 100.
The power density makes use possible in a handheld electric machine
tool 10 with sufficient power delivery of tool 60.
[0055] Activation of tool 60 by activation actuator 30 may be
indicated by a signal element 122 (FIG. 2).
[0056] In FIG. 1, electronic unit 200 is integrated in a
particularly space-saving manner on a single printed circuit board
210. In FIG. 2, the electronic unit is divided between two printed
circuit boards 212, 214, one being disposed in the main part and
one being disposed in the grip part of T shaped housing 20, which
grip part juts out at right angles to the main part.
Advantageously, drive unit 80, electronic unit 200 and operating
voltage unit 90 are distributed in housing 20 in such a way that a
center of gravity lies in the region of grip part 40.
[0057] FIG. 3a shows an outline sketch of an activation of
excitation actuator 100, for example in the form of piezo actuator
100, with an AC voltage power supply from a mains supply network or
with a DC voltage power supply with a battery pack.
[0058] When electronic unit 200 has a mains power supply, for
example 220 Volt AC, a component assembly 94 is provided that
rectifies and smoothes the AC voltage. Electronic unit 200 includes
a power generating unit 222 into which the DC voltage is fed and
which is coupled to excitation actuator 100 via a suitable filter
unit 226. A regulating unit 224 provides the regulating signals for
excitation actuator 100. The operating frequency of excitation
actuator 100 is in the range of from 10 kHz to 1000 kHz, preferably
from 30 kHz to 50 kHz, and especially from 35 kHz to 45 kHz, more
especially around 40 kHz.
[0059] If power is supplied by operating voltage unit 90 using
non-rechargeable or rechargeable batteries 92, it is possible to
reduce the space required, since it is possible to omit component
assembly 94 for rectifying and smoothing. The electrical output
voltage of operating voltage unit 90 is preferably below 100 Volt,
and is approximately 36 Volt or 10.8 Volt.
[0060] The maximum electric excitation field strength of the at
least one excitation actuator is preferably in the range below 300
V/mm (based on the thickness, especially disc thickness, of the
piezoelectrically active material), preferably in the range of from
50 V/mm to 220 V/mm. At a disc thickness of excitation actuator 100
of typically from 1 mm to 10 mm, preferably 2 mm to 6 mm, and
especially of around 5 mm, the electrical voltages are below 1000
Volt.
[0061] In one embodiment variant, power generating unit 222 may be
implemented by 4 MOSFET semiconductors in a conventional full
bridge topology. In a further variant, the generation of the
operating signal may also be effected by a conventional half bridge
topology with, for example, a mid point capacitor for filtering the
DC component.
[0062] FIG. 3b illustrates one possibility for making the overall
size of filter unit 226 as small as possible. For that purpose,
power unit 222 may be driven by regulating unit 224 in such a
manner that, by sine-triangle modulation for example, it generates
instead of simple square-wave signals a square-wave voltage that is
more similar to a sine. Depending on the level of the clocking,
that is, the number of individual pulses that together reproduce a
sine, the content of undesirable harmonics may be distinctly
reduced, which results in a smaller design of filter unit 226. For
this, the number of square-wave pulses per cycle duration of the
sinusoidal signal is greater than 6, preferably in the range of
from 6 to 100, especially in the range of from 10 to 26. In one
embodiment variant, the number and width of the square-wave pulses
of regulating unit 224 may also be varied during operation, for
example with changes in load.
[0063] FIG. 4 shows a progression of an ultrasound amplitude along
an excitation actuator 100 in the form of a piezo actuator.
Coupling element 106 is in the form of a sonotrode. The region of
excitation actuator 100 adjoining piezoelectric material 102 is
referred to together with piezo discs 102 as a converter.
Piezoelectric material 102 is excited by the supplied
high-frequency AC voltage into oscillations which are transmitted
into coupling element 102 via the converter. In the case of a
three-stage structure of excitation actuator 100 such as that shown
in FIG. 4, excitation actuator 100 additionally consists of a
booster 104 for amplitude matching. Along the length M of
excitation actuator 100 the amplitude Amp of the excited
oscillation increases on average. Variations in the resonant
frequency f_res of the oscillating system of excitation actuator
100 (where applicable with attached tool) during operation are
preferably compensated for, for example using a phase regulating
chain already described above with which the phase shift between
the electrical voltage fed into excitation actuator 100 for
excitation thereof and the electrical current fed in is regulated
to zero (phase zero regulation), or using a maximum regulation of
the electrical current fed into excitation actuator 100.
[0064] FIG. 5 shows an impedance characteristic of an excitation
actuator implemented by a piezo actuator with the resonant
frequencies f_res and f_res2. Curve A shows the variation of the
impedance Imp as a function of the frequency f, which passes
through an impedance minimum at resonant frequency f_res and
through an impedance maximum at f_res2. The frequency f_res is
referred to as series resonance, and f_res2 as parallel
resonance.
[0065] Curve B shows the variation of the phase shift between
current and voltage, which has a zero crossing at the resonant
frequency and changes from -90.degree. below the resonant frequency
f_res to +90.degree. above the resonant frequency f_res. On passing
through the parallel resonance f_res2, the phase shift changes from
+90.degree. below the resonant frequency to -90.degree. above the
resonant frequency.
[0066] For signal filtering and for inductive compensation of the
at least one excitation actuator 100, at least one inductance may
be provided in a power circuit of the electronic unit, which
circuit acts upon the at least one excitation actuator 100 with
electrical power. It is possible to obtain a space-saving layout of
the power inductances together with the transmission transformer in
a single coil core. The signal filtering and inductive compensation
of the piezo actuator, which is beneficial in the case of
excitation actuators 100, may be provided directly by a
specifically adjusted stray inductance of a transmission
transformer that is required in any case, or may be afforded by an
inductance wound on the same coil core. An additional coil core
with a further inductance in the power circuit may thereby be
omitted.
[0067] To illustrate this, FIG. 6 shows an equivalent circuit
diagram with an ideal transformer. The inductance M is used for the
actual transfer from primary side to secondary side. The stray
inductances occur since it is never possible for the windings to be
ideally coupled. L1 and L2 form the part of the magnetic field that
cannot be "captured" by the secondary coil. L1 and L2 are to be
regarded in electrical terms as being like an air-core coil.
[0068] Electric machine tool 10 shown as an angle grinder in FIG. 7
includes a housing 20 consisting of a motor housing 22 and a grip
housing 24, a damping element 26 being disposed between motor
housing 22 and grip housing 24. Electric machine tool 10 is held at
grip housing 24 which forms grip area 40. Motor housing 22 houses a
drive unit 80 with a drive component in the form of an electric
drive motor 82 which is coupled to and drives a tool shaft 64 via a
gear unit 62. Tool shaft 64 is the carrier for a tool 60, in the
form of a grinding wheel, which is fastened interchangeably to tool
shaft 64.
[0069] In FIG. 8, tool shaft 64 and tool 60 fastened thereto in the
form of a grinding wheel are shown in a detail view. Tool shaft 64,
which has longitudinal axis L, is rotatably supported in bearings
70 and 72 spaced apart from each other in housing 20. Situated on
tool shaft 64 at the opposite end face from the grinding wheel,
there is a beveled wheel 74 via which tool shaft 64 is driven by
electrical drive motor 82.
[0070] To reduce the size of the chips produced during machining of
a workpiece with tool 60 in the form of a grinding wheel, tool 60
in the form of a grinding wheel is set into high-frequency
oscillation in addition to its rotary working motion. This involves
superimposed oscillations which are superimposed on the working
motion of tool 60 in the form of a grinding wheel. Those
superimposed oscillations are generated with the aid of excitation
actuator 100 which is also disposed in housing 10 of handheld
electric machine tool 10 as a further drive component of drive unit
80 and which directly or indirectly excites tool 60 in the form of
a grinding wheel into the superimposed oscillations. In the
exemplary embodiment shown in FIG. 8, excitation actuator 100 acts
upon tool-side bearing 70 of tool shaft 64 and generates
superimposed oscillations that are directed orthogonally to
longitudinal axis L of tool shaft 64. Those superimposed
oscillations directed orthogonally to longitudinal axis L are also
transmitted via tool shaft 64 to tool 60 in the form of a grinding
wheel which similarly executes superimposed oscillations
orthogonally to longitudinal axis L and thus in its plane of
motion.
[0071] It is also possible for excitation actuator 100 to be
positioned at a different location, for example at bearing 72
remote from the tool or directly at a position on tool shaft 64 or
on tool 60 in the form of a grinding wheel in order for tool 60 to
be acted upon directly by superimposed oscillations.
[0072] Various active actuators may be used as excitation actuator
100. Preference is given to the use of actuators that generate
high-frequency oscillations in the ultrasound range, especially in
a frequency range of at least 20 kHz, but with frequencies in
higher orders of magnitude coming into consideration, especially up
to and including the megahertz range, or also smaller
frequencies.
[0073] By way of example, there is used as excitation actuator 100
a piezo element whose length changes as a result of application of
an electrical voltage. Since piezo elements respond very rapidly to
voltage changes, by applying a high-frequency voltage it is
possible to produce a correspondingly rapid change in length in the
excitation actuator, which exerts an effect on tool 60 which by way
of example is in the form of a grinding wheel here.
[0074] Excitation actuator 100 may also be in the form of a
magneto-resistive actuator in which the electrical resistance is
changed by application of an external magnetic field.
[0075] In the exemplary embodiment shown in FIGS. 8 and 9, the
superimposed oscillations are generated in the direction of arrow
110, orthogonally to longitudinal axis L of tool shaft 64 and tool
60 in the form of a grinding wheel. In the exemplary embodiment
shown in FIG. 10, on the other hand, excitation with the
superimposed oscillations takes place in accordance with arrow
direction 110, in the direction of longitudinal axis L of tool
shaft 64 and tool 60 and thus perpendicularly to the plane of
motion of tool 60 in the form of a grinding wheel. Excitation
actuator 100, by which the superimposed oscillations are generated,
acts either directly upon tool shaft 64 or one or both bearings 70
and 72 or directly upon tool 60 with the superimposed oscillations
in the axial direction.
* * * * *