Oscillators – Electromechanical resonator – Crystal
Patent
1992-07-13
1994-03-15
Grimm, Siegfried H.
Oscillators
Electromechanical resonator
Crystal
310317, 318116, 331177R, 331181, 366116, B06B 102, H03L 700
Patent
active
052948960
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a system for driving a tool arrangement which oscillates at high frequency, and then particularly to a system for driving a tool tip which is intended for working a workpiece and which oscillates at high frequency and which can exhibit a resonance pattern when driven with the aid of an alternating voltage to which a particular frequency is assigned, a so-called resonance frequency.
Tool configurations which include readily attached and detached tool tips of the aforedescribed kind are previously known and include a device, such as a piezoelectric crystal, which changes form when subjected to changes in the voltage and in which the crystal is influenced by an electric drive circuit which is constructed to generate an alternating voltage whose frequency normally lies within the range of 20-40 kHz.
Tool configurations of this kind normally include a holder or handle which surrounds the crystal and holds the crystal firmly clamped, and to which there can be fitted a tool tip, such as a chisel, a file, grinding meant and the like, by means of which a workpiece can be worked and which are intended to be moved reciprocatingly during the actual working process.
BACKGROUND ART
Each tool arrangement of the aforesaid kind intended for driving a high-frequency oscillating machine tool comprising one or more crystals which change their form when subjected to a change in voltage and which are incorporated in a tool holder and which utilize an electric drive circuit constructed to produce an alternating voltage which can be applied to the crystal, is fitted with a tool tip.
As a result of its construction, the material from which it is made, and its size and shape, each such tool tip, has a resonance frequency at which the energy losses are low. However, when pressure is brought to bear on the tool tip as it performs work, the resonance frequency will change momentarily and consequently there have been proposed various control circuits or regulating circuits (first control circuits) which strive to cause the high frequency oscillation or the alternating voltage applied to the crystal to lie in a momentary resonance frequency. In principle, the resonance frequency is determined electrically by two parallel-connected electrical oscillation circuits, where a first resonance circuit can be considered to constitute a capacitance and an inductance value which is dependent on the extent to which the tool tip is loaded, and therewith varies in time, and where a second resonance circuit can be considered to comprise a substantially fixed capacitance belonging to or related to the crystal and a substantially fixed inductance incorporated in the drive circuit.
It is also known that a given change in resonance frequency will occur as a result of operating conditions and when the tool tip is loaded. This change is normally of such small magnitude that the aforesaid second resonance circuit, with said fixed inductance, will still function very effectively provided that the tool tip is suitably adapted to a selected resonance frequency and provided that the operating conditions are suitably selected within narrow limits.
It has also been proposed to use a frequency controllable supply voltage whose frequency can be adapted to momentary resonance frequencies, by using a first control circuit.
Previously known constructions of this kind enable frequency to be controlled or regulated within narrow limits, say +/-2 kHz, since one control circuit, constructed to detect and regulate towards a fixed minimum impedence, can readily slide over resonance criteria (100 at FIG. 6B) and when detecting and regulating towards a prevailing phase position, between the current and voltage values, there is no positive impedence phase around the series resonance (200 and 200' at FIG. 6B and 6C).
It has been found, however, that when such a drive circuit construction is used at very high loads and/or at prevailing idling frequencies which lie adjacent the resonance frequency and at moderate load, there is
REFERENCES:
patent: 4168916 (1979-09-01), Yamada et al.
patent: 4965532 (1990-10-01), Sakurai
patent: 4970656 (1990-11-01), Lo et al.
Kjellander, deceased Jan
Lundberg Jan
Nilsson Thord
Diprofil AB
Grimm Siegfried H.
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