Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1993-07-19
1995-01-31
Budd, Mark O.
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
310325, 209346, 2093651, H01L 4108
Patent
active
053861698
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a device for causing one or more untuned structures to vibrate ultrasonically. These structures may be of very different types, but the present description will be essentially limited to a screening structure, although this must not be interpreted as limiting the present invention.
It has been known for many years that causing a screen to vibrate ultrasonically effects a qualitative and quantitative improvement in the screening of fine powders or fine materials considered difficult to process.
Consider for example the problems encountered with mineral, metal and ceramic powders, with particle sizes in the order of one micron and less, and with spheroidal granules which tend to clog the screens. Ultrasonic techniques have already been described in the literature of this art and in particular in the work entitled Crowford Engineering of Frederick and Co.
The state of the art is also shown by FR-A-2 233 108 which describes screening equipment provided with an ultrasonic transducer in direct contact with the filter cloth.
Note that a device of this kind is restricted to circular screens. As ultrasound is emitted from a single anchor point the mesh is subject to non-negligible stresses at this level which may cause premature wear and consequential pollution of the product treated.
In the case of a multistage screen the number of transducers must be multiplied commensurately and this complicates the construction. This prior art device has another drawback in that, in all cases, the converter is exposed to direct contact with the treated product and must usually be sealed.
The document DE-A-38 13 178 discloses a device for causing to vibrate at an ultrasonic frequency a structure comprising at least one electro-acoustic converter adapted to vibrate in a given vibration direction and fixed rigidly to said structure by means of metal fixing members tuned to the converter frequency, the links with the structure being in a region of maximum amplitude of said fixing members.
An object of the present invention is to provide an ultrasonic vibrator device which circumvents all the drawbacks of the prior art devices.
The main aim of the present invention is to render a support structure resonant. This is, for example, a filter cloth, membrane or other plate support which is not resonant in itself at the frequency of the ultrasonic emitter.
Another aim of the ultrasonic device in accordance with the invention is to optimize the ultrasonic efficiency regardless of the shape and size of the structure to be caused to vibrate. Naturally a main objective of the present invention is to prevent direct contact of the ultrasonic transducer with the filter cloth or membrane. In the case of a screen, the device in accordance with the invention excites the mesh by means of ultrasonic energy previously distributed in its supporting frame, so minimizing stresses at the anchor points. Finally, as explained in more detail later in this description, the ultrasonic device in accordance with the invention may be fitted to existing structures by modifying the geometrical shape of coupling members tuned to integer multiples of the half-wavelength at the output frequency.
In accordance with the present invention these objectives are achieved by a device for causing an untuned structure to vibrate at an ultrasonic frequency which is characterized in that it comprises at least one electro-acoustic converter fixed rigidly to said structure by means of metal fixing members tuned to the frequency of the converter, the structural couplings being located in a maximum amplitude region of said fixing members and the assembly being made resonant by fixing a nut or any other metal assembly tuned to an integer multiple of the half-wavelength.
Other features and advantages of the present invention will emerge from the following detailed description with particular reference to embodiments shown in the appended drawings in which:
FIGS. 1 and 2 show two different types of coupling bar profile for matching dimensional constraints
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