Vibration reduction

Details Vibration reduction Vibration reduction

1995-02-10

1996-03-05

Dougherty, Thomas M.

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

310326, 310331, 310367, H01L 4108

Patent

active

054970431

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to a method of vibration reduction and apparatus for the same based on the technique of cross axis actuation.
Discussion of Prior Art
Cross axis actuators are used for the active control of vibration in various pieces of apparatus, in particular elongate members, and operate to isolate vibration to a particular part of an apparatus by actively deforming an element along which undesirable vibrations are transmitted.
Various approaches to the active control of vibration transmitted along elongate members are known. UK patent application, publication number 2229789 discloses the use of a plurality of elongate and rigid actuators which are attached in parallel across a length of elongate member. The elongate member has flanges anchored to it at two points along its length and the actuators are then attached to the flanges. The actuators are movable via control signals originating from sensors so as to cause small deformation in the member between the points of flange attachment. This results in vibrational energy being reflected back towards its source. By attaching six actuators it is possible to control all possible low frequency vibrations which the member undergos, that is, longitudinal (compressional), transverse and torsional vibrational modes. In this case each flange has three attachment points for the actuators the attachment points on each flange being positioned at an angle of 120.degree. to each other relative to the axis of the member. The relative attachment points on one flange to the other are offset by an angle of 60.degree. with respect to the axis of the member. Each flange attachment point serves to attach two actuators these actuators being attached to the two closest attachment points on the other flange.
This design is however rather complex and costly. It also occupies a significant volume within the region of the flanges and this may hamper fitment of the device and its maintenance.
There is therefore a requirement for a simplified approach to the design of cross axis actuators occupies less space in the region of attachment.


SUMMARY OF THE INVENTION

According to the present invention there is provided a cross axis actuator for reducing the transmission of vibration along elongate members and the like which comprises a series of windings wound around the member along at least part of the members length in clockwise and anti-clockwise fashion and are anchored at two or more points to the member, the windings being subject to strain in order to cause deformation of the member in at least part of the regions between attachment points.
Preferably, the clockwork and anti-clockwork windings around the member are wound in a helical fashion.
Preferably, the pitch of the windings is at about 30.degree. to the longitudinal axis of the elongate member, although this is not critical and other pitches may be adopted depending upon the degree of control of deformation required.
Typically the member will be a steel pipe or rod but the invention is not limited in this respect and may be used on a variety of structures which are capable of transmitting unwanted vibrations and to which the invention may reasonably be applied. The member could be a tube or pipe filled with a fluid. In such a case, it is possible for the fluid to be either stationary or flowing in a particular direction through the pipe.
Preferably, the windings are provided in the form of wires which are ideally formed from steel. Alternatively, strips of material can be used for the windings. Ideally, the numbers of windings wound around the member in a clockwise and anti-clockwise direction are equal.
Whilst the windings may be attached to the member at the minimum two points it is preferred that they are attached to the member on a continuous basis with the exception of having the ends of the windings free.
The strain generated in the windings can be provided in various ways. There are two preferred options. One option is to provide the strain in the windings by attaching a

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"A New Type of Piezoelectric-Ceramic Hollow-Cylinder Torsional Vibrator" by H. Shimizu et al., pp. 104-105, Japanese Journal of Applied Physics vol. 29, Nov. 1989.
IBM Technical Disclosure Bulletin-"Electroacoustic Transducers for Optical Fiber Modulator and Tap" by F. G. Feller, vol. 21 No. 2 Jul. 1978, pp. 813 and 814.

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