GB2333457A - Extendible arm including magneto-strictive element - Google Patents

Abstract

This is an arm which does not require direct access to it (such as leads or mechanisms) in order to perform controlled extensions. An example is in the medical application where link arms are used to extend limb bones. Here regular extension of the bone is needed without perforation of the surrounding tissue. This link arm is secured to the bone, and completely encased within the limb. Placing the limb in a strong cycled magnetic field energises the magneto-strictive element 5, which allows part 6 to move with respect to part 3. The unit has lock mechanisms 4 which allow movement in only in the extension direction.

Description

EXTENDIBLE ARM This invention relates to an extendible arm.

Extendible arms are used in many applications ranging from precision actuators to coarse adjusters. In powered applications the energy is provided by direct connection to the arm. Magneto-strictive actuators are self-contained units, with leads by which their coil is energised. Applications exist where extendible arms are required, where connection to the arms is inconvenient.

An example is in medical applications such as bone links. Extendible bone links are often made to protrude the patients skin, where extender mechanisms can access the link for extension.

The present invention allows powering of the extendible link without the need for direct connection, as long as the intervening material is permeable to the energising medium.

The accompanying schematic drawings show the principle of operation of the invention. In the example of a link to extend the bone of a limb, components 3 and 6 would be attached to the bone, and part 2 would be tissue between the bone and up to the skin. To extend the arm the coil is repeatedly energised and de-energised. Each time this is done the arm extends in length. This is done in small extension steps of a controllable size, which are proportional to the magnetic field strength..

In Figs. 1, 2 and 3 the arm length is determined by the relative positions of parts 3 and 6. Part 5 is the magneto-strictive section, which changes length with the application of the magnetic field of part 1, the coil. Part 2 is obstructing material which is permeable to the magnetic field. Parts 4 are locking mechanisms. These can move only in one direction along part 6, and will lock when forces try to compress the assembly.

The arm can be extended, even when completely encapsulated in the material of part 2.

Claims (5)

1. CLAIMS 1. An arm, which can be extended in length when completely encased in a magnetic field permeable material.
2. 2. An arm, as in claim 1, which can be extended without need for perforation of the encasing material.
3. 3. An extendible arm, as in claim 1, which self-locks upon reaching a new extended length.
4. 4. An extendible arm, as in claim 1, which extends in controlled extension steps.
5. 5. An extendible arm, as in claim 1, whose operating principle is schematically represented by figures 1, 2 and 3 of the accompanying drawing.