Machine element or mechanism – Mechanical movements – Oscillation or reciprocation to intermittent unidirectional...
Patent
1992-07-23
1993-12-07
Herrmann, Allan D.
Machine element or mechanism
Mechanical movements
Oscillation or reciprocation to intermittent unidirectional...
74106, 74585, 188 2412, 310 92, H02K 3500
Patent
active
052674797
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a force actuator arrangement comprising a force generating member performing a reciprocating axial movement, force transmitting means intended to apply a force by unidirectional movement in an application direction and a device for transforming the reciprocating movement to the unidirectional application movement
TECHNICAL BACKGROUND
In a number of different ways it is possible to accomplish a reciprocating movement or force, which it may be desirable to transform into a unidirectional movement or force. A relatively recently developed technique is to utilize materials having magnetostrictive properties. Magnetostriction means that a material changes its dimensions when exposed to a magnetic field.
Materials with such properties are typically alloys with rare earth metals, an alloy with terbium and iron being available under the name Terfenol. This material Terfenol has a very high magnetostriction, namely up to 0.2% at a magnetic field with a field strength of appr. 3000 oersted, and a very fast response.
Due to the magnetostriction a Terfenol rod exposed to a pulsating magnetic field and prestressed for accomplishing a return to original shape will have reciprocating length and accordingly exert an reciprocating force.
In order to utilize this reciprocating movement or force in a practical force actuator this movement has to be transformed--by a movement transforming device into a unidirectional movement of a push rod or the like in the actuator.
The Invention
In order to allow such a movement transforming device to perform its intended function to create a unidirectional movement from a reciprocating movement, the arrangement according, to the invention is characterized in that the reciprocation frequency of the force generating member is higher than the natural frequency of the force transmitting means for enabling the movement transforming device to transmit the movement only during each reciprocating stroke in the application direction.
In this way the movement transforming device will disconnect the force transmitting means, which in a disc brake arrangement include the caliper, from the force generating member--a Terfenol rod--during each reciprocating stroke in the direction opposite the application direction, so that a step-wise application movement with extremely small steps is obtained. In a practical embodiment of a disc brake arrangement the Terfenol rod may have a reciprocating frequency of 1000 Hz, whereas the natural frequency of the disc brake caliper may be 130 Hz.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in further detail below reference being made to the accompanying drawings, in which FIG. 1 shows a rather simple embodiment of a disc brake with an actuator according to the invention, FIG. 2 is a side-view, mostly in of another embodiment of an actuator for an arrangement according to the invention, FIGS. 3 and 4 are side-views, partly in section, of two modified devices for use in an actuator according to FIG. 2, and FIG. 5 is a side-view, mostly in section, of still another embodiment of an actuator for an arrangement according to the invention.
DETAILED DESCRIPTION OF EMBODIMENTS
FIG. 1 shows a simple disc brake arrangement, which illustrates the invention.
The arrangement is intended to brake a rotating disc 1 by means of brake pads 2 arranged at the ends of two caliper levers 3 and 4 pivotally attached to each other at 5. The braking action is obtained by pushing the ends of the levers 3 and 4 opposite the pads 2 apart.
In the simple arrangement according to FIG. 1 this is accomplished by an electric coil 6 surrounding a rod 7 of the material called Terfenol, with the characteristics to prolong itself up to say 0.2% of its length when subjected to a certain magnetic field (from the coil 6). The rod 7 is connected to the lever 3 to the left in FIG. 1 and cooperates with the lever 4 to the right via a wedge 8. The wedge 8 is biased upwards by a compression spring 9 and cooperates with a wedge surface in
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Brown Laurence R.
Herrmann Allan D.
SAB WABCO AB
Trousdell William O.
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