Recorders – Markers and/or driving means therefor – Printing – dotting – or punching marker
Reexamination Certificate
1999-07-27
2001-12-18
Barlow, John (Department: 2853)
Recorders
Markers and/or driving means therefor
Printing, dotting, or punching marker
C400S124160
Reexamination Certificate
active
06331037
ABSTRACT:
The invention relates to a drive arrangement, for example for a writing head, comprising a piezoelectrically actuated lever arrangement for moving a writing tip in the direction of a recording medium when writing on the recording medium. This drive arrangement can also be used in accordance with the invention as a positioning drive for a series of other applications, and can also be used in accordance with the invention as a signal generator.
The writing head which comprises at least one writing tip for writing on a recording medium can, for example, be used to apply ink to a recording medium, such as paper, with the recordings representing alphanumeric text and/or measured values. A plurality of writing tips can be used in order to print inks of different colors. However, it is not essential to use ink since recordings can also be produced thermally or by pressure on a suitably sensitive recording medium. The recordings on the recording medium can either be discontinuous, for example dots, or continuous, for example a line. The recordings can also be traces which are to be recorded for protocol or measurement purposes.
Discussion of the Prior Art
A writing head of the initially named kind is, for example, known from DE-OS-38 32 564. The movement of the writing tips against a recording medium takes place there via a lever arm which follows the movement of a piezoelectric actuator. This actuator comprises an arm which is realized in the form of a bending piezoelectric oscillator element (in the manner of a flexible tongue) which is manufactured of a sintered ceramic material. The oscillating element has a longitudinal dimension which is much greater than its cross-section so that it is elastically deformable. One end of the tongue is secured to the body of the writing head so that, when the piezoelectric oscillator element is excited by a suitable control signal, the free end of the tongue moves in the direction perpendicular to its longitudinal axis. The free end of the tongue is connected to the lever arm which can rotate up to a certain degree about an axis. On application of the control signal to the oscillating element, the end acting on the lever arm moves and swings the lever arm about its point of rotation and its forked free end drives the writing tip. This is lifted and lowered thereby in relation to a roll guiding the recording medium, with ink, which is periodically supplied from a reservoir via a feed tube to the writing tip, being applied by the latter onto the recording medium.
The construction of DE-OS 38 32 564 achieves only a small step-up via the lever arm. The expansion of the piezoelectric oscillator element is essentially itself responsible for the amplitude of the movement of the writing tip, i.e. this amplitude depends on the movement of the piezoelectric arm itself.
It is a problem with this known arrangement that a frequent and rapid to and fro movement of the piezoelectric oscillator elements, which themselves represent a part of the lever arrangement, causes fatigue which is worsened by the fact that their cross-section is very small in comparison to their length dimension. Accordingly, the piezoelectric oscillator elements break easily and frequently. This leads to a complete or partial destruction of the writing head and the printer cannot be used until the damage has been repaired. Moreover, these tongue-like piezoelectric oscillator elements are relatively expensive because they are manufactured in relatively small numbers and this makes the writing head more expensive.
The resetting of the piezoelectric tongue, which is brought about by an applied voltage, is also problematic. If the current supply is switched off, or if a fault occurs, the flexible tongue moves to a position closer to the recording medium and a situation can arise in which the writing tip contacts the recording medium and ink runs out which leads to soiling.
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is to realize a favorably priced and operationally reliable drive arrangement of the initially named kind and to ensure a long working life with a mechanical resetting of the drive arrangement preferably taking place automatically. The drive arrangement should also be suitable as a positioning drive and can serve in inverse form as a signal generator.
In order to satisfy this object, a piezoelectric actuator separate from the lever arm arrangement is used, with the lever arrangement exerting a compressing force onto the piezoelectric actuator.
Expressed differently, a drive arrangement of the initially named kind is provided in accordance with the invention and is characterized in that the piezoelectric actuator is arranged in a yoke, in that the yoke exerts by spring action a compressive force onto the piezoelectric actuator and is designed as a step-up transmission, or as part of a step-up transmission, which follows at its input, on electrical energization of the piezoelectric actuator, the change of length of the actuator as an input movement and has an amplitude of motion at its output side which is a plurality of times greater.
The invention enables the use of customary piezoelectric elements for the actuator, so that the fragile and expensive tongue-like piezoelectric ceramic actuator in accordance with the prior art can be avoided. It is intended that the expression “piezoelectric actuator (or PZ actuator)” covers the use of one piezoelectric element or of a plurality of piezoelectric elements.
In the present invention the PZ actuator preferably comprises a stack of piezoelectric elements, for example in the form of discs or plates, which are stacked face-to-face along an axis which extends perpendicular to the aligned parallel faces of the elements. Because each piezoelectric element expands fractionally when a drive voltage is applied, the individual expansions of each PZ element along the axis add up, whereby a resulting movement of greater amplitude arises. This movement, which can for example amount to 5&mgr; is then further enlarged by the step-up transmission, for example by about 400 times, whereby an amplitude of movement of about 1.5 mm can be achieved on taking account of the deformations and tolerances that arise, which is straightforwardly sufficient for the actuation of the writing tip. Since the lever arrangement advantageously exerts a compressing force onto the piezoelectric actuator, for example of a stack of piezoelectric elements, a more robust and stable arrangement arises for the same degree of movement as in the arrangement known from DE-OS 38 32 564 while using customary (for example commercially available) piezoelectric elements. It is therefore more effective but less expensive and more durable than the arrangement of the prior art.
It is particularly favorable that the forces which arise through expansion of the piezoelectric elements do not act externally, i.e. are, so to say, internally taken up in the yoke or frame, if required by the step-up transmission, and thus do not act on the housing of the writing head or on the pivot axles and guides contained therein. With the compact dimensions of the writing head of the invention this is a significant advantage in comparison to the prior art, since even relatively small unbalanced forces could lead to deformations and faulty behavior of the writing head.
Moreover, the use of a force which compresses the piezoelectric elements leads in a favorable manner to a mechanically defined reset position of the actuator and thus of the writing tip.
The PZ actuator (for example a stack of PZ elements) is preferably compressed between a movable part of the lever arm and a fixed part of the arrangement. It can for example be mounted between a section of a lever arm and a carrier secured to the writing head. It is preferably compressed in a U-shaped yoke or closed frame which expands when the Pz actuator is excited. With one embodiment of the invention a U-shaped or C-shaped yoke which has a unitary flexible section (which acts as a hinge or joint) engages around the PZ actuator element so
Gebert Norbert
Reinold Udo
Roscher Dietrich
ABB Instrumentation Limited
Barlow John
Cowan Liebowitz & Latman PC
Gable R. Lewis
Stephens Juanita
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