Title:
HANDHELD ELECTRIC MACHINE TOOL
Kind Code:
A1


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)
Application Number:
13/142696
Publication Date:
02/23/2012
Filing Date:
12/17/2009
Assignee:
ROSER JOCHEN
DELFINI STEFANO
KOEDER THILO
PLATZER JOACHIM
SPREMO IVAN
Primary Class:
Other Classes:
173/2
International Classes:
B24B23/00; B24B49/10
View Patent Images:
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Primary Examiner:
TRUONG, THANH K
Attorney, Agent or Firm:
Hunton Andrews Kurth LLP/HAK NY (200 Park Avenue New York NY 10166)
Claims:
1. 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 cm3.

33. The handheld electric machine tool as recited in claim 31 wherein a volume of the piezoelectric material is at least 0.5 cm3.

34. The handheld electric machine tool as recited in claim 31 wherein a volume of the piezoelectric material is at least 1 cm3.

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/cm3, 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/cm3.

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 μm.

38. The handheld electric machine tool as recited in claim 37, wherein the oscillation amplitude is at least 8 μm.

39. The handheld electric machine tool as recited in claim 37, wherein the oscillation amplitude is at least 12 μm.

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

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

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.

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

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.

The electronic unit is configured to operate the at least one excitation actuator in a resonant frequency.

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.

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.

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° phase difference between current and voltage signal, thereby enabling an optimum power yield to be achieved.

In accordance with an advantageous development of the present invention, the volume of the piezoelectrically active material may be at least 0.2 cm3, preferably 0.5 cm3, especially at least 1 cm3. Advantageously, it is possible for a sufficient ultrasound power to be achieved with a small overall size of the excitation actuator.

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/cm3, preferably at least 20 Watt/cm3, 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.

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 μm, preferably at least 8 μm, especially at least 12 μm. 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.

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.

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.

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.

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 Umains (effective value of mains voltage) to 2 Umains. Preferably, for example with the use of a bridge rectifier with smoothing capacitor, 1.4 Umains. In a further embodiment, the mains voltage may be transformed using an input-side transformer to a voltage suitable for the operating voltage unit.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

FIG. 1 shows an exemplary embodiment of a handheld electric machine tool configured as a cutting tool.

FIG. 2 shows a further exemplary embodiment of a handheld electric machine tool configured as a drill.

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).

FIG. 4 shows a progression of an ultrasound amplitude along a sonotrode.

FIG. 5 shows an impedance characteristic for detecting a resonant frequency of an excitation actuator.

FIG. 6 shows an equivalent circuit diagram of an ideal transformer.

FIG. 7 is a sectional view of an electric machine tool in the form of an angle grinder.

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.

FIG. 9 shows the grinding wheel of FIG. 8 with bearing and excitation actuator in plan view.

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

In the Figures, components that are identical or of the same kind are numbered with identical reference numerals.

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.

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.

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.

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 λ/2 of the ultrasonic oscillation. Other embodiment variants may provide that excitation actuator 100 is composed of a plurality of components of length λ/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.

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.

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°. 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.

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 cm3, preferably 0.5 cm3, especially at least 1 cm3. Excitation actuator 100 may have a power density of at least 5 Watt/cm3, preferably at least 20 Watt/cm3, 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.

Activation of tool 60 by activation actuator 30 may be indicated by a signal element 122 (FIG. 2).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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° below the resonant frequency f_res to +90° above the resonant frequency f_res. On passing through the parallel resonance f_res2, the phase shift changes from +90° below the resonant frequency to −90° above the resonant frequency.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.