Microactuator arrangement

Details Microactuator arrangement Microactuator arrangement

2002-09-27

2004-02-03

Nguyen, Hoang (Department: 3748)

Power plants

Motor operated by expansion and/or contraction of a unit of...

Mass is a solid

C060S528000

Reexamination Certificate

active

06684638

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a micro actuator arrangement including a substrate having a first thermomechanical micro actuator and a second thermomechanical micro actuator, wherein the first thermomechanical micro actuator is extended substantially in parallel with the surface of the substrate in response to a thermal stimulation. The micro actuator arrangement is particularly well suitable for the application as micro relay.
Micro relays are taking the place of conventional electromechanical relays to an ever-increasing extent because they can be manufactured as lower costs and at a reduced space required and as they achieve moreover shorter switching intervals due to their size. At present, these micro relays are normally realised on the basis of micro actuators operating on the principle of electrostatic effects. These electrostatic micro relays, however, excel themselves by comparatively short positioning travels and small activation forces of the micro actuators, which, on the one hand, results in problems in terms of the disruptive strength of the micro relay and, on the other hand, leads to problems caused by an increased contact wear.
By contrast, thermomechanical micro actuators, which are used in other fields of micro system technology, are characterised principally by the generation of comparatively high activation forces and long positioning travels with simultaneous moderate power consumption. They are used in micro system technology mainly for the design of micro actuator elements where a maximum possible of actuating forces and positioning travels is decisive. One example is the application in micro valves. As electrical power levels in the range of a few 100 mW are required, as a rule, for the operation of thermal micro actuators thermal drive systems have so far come into question mainly for the structure of individual actuator elements.
The fact that a thermomechanical micro actuator must continuously be heated by supplied energy in order to maintain its extended state (ON state), which is achieved by thermal stimulation, has, however, turned out to be a particular disadvantage. For this reason, thermomechanical micro actuators have so far not been used or used only in cases of exception in micro relays and in a great number of other applications.
PRIOR ART
The U.S. Pat. No. 5,909,078 discloses an example of a micro actuator arrangement including thermomechanical micro actuators in accordance with the introductory clause of patent claim 1. Here, an individual element or a plurality of bar-shaped elements in a side-by-side arrangement is/are used as micro actuators, which are clamped in parallel with a substrate surface on the substrate on both ends and which are biased in parallel with the substrate surface in a preferential direction. When the bar-shaped elements are heated they extend in the clamped condition so that a extension in the preferential direction results in parallel with the substrate surface. This extending movement may be used, for instance, for opening or closing a valve opening in the substrate.
The thermomechanical micro actuators of that prior art document can, however, not be used without occurrence of the aforedescribed disadvantages in a micro relay in which separate switching conditions must be retained over a major period of time.
The thermomechanical micro relay that is described by J.-Y. Lee et al. in “A characterization of thermal parameters of thermally driven polysilicon micro bridge actuators using electrical impedance analysis” in “Sensors and Actuators” A75 (1999, pp. 86-92, presents the same disadvantage. In that relay, a poly-silicon membrane having a bridge-like configuration is extended by heating in a direction orthogonal on the substrate surface in order to connect electrical contacts. However, a permanent energy supply is required to maintain this connection.
The prior art document WO 99/16096 discloses a micro relay composed of a plurality of thermomechanical actuators having the same structure and clamped, by means of bar-shaped elements, to the respective two ends on the substrate. The heating of the bar-shaped elements causes a extension of the two actuators in parallel with the substrate surface. Via mechanical locking mechanism, i.e. lateral hooking to the second actuator, it is possible to keep one of the actuators in a defined position in a de-energized state. The locking action can be eliminated again by operation of the second actuator.
Starting out from this prior art, the problem of the present invention consists in proposing a further micro actuator arrangement that permits a change-over between at least two switching states with a high activation force and a long positioning travel, with the possibility to maintain the respective switching conditions without power consumption.
BRIEF DESCRIPTION OF THE INVENTION
The problem is solved with the micro actuator arrangement according to patent claim 1. Expedient embodiments of the micro actuator arrangement are the subject matters of the dependent claims.
The present micro actuator arrangement consists of a substrate comprising at least two thermomechanical micro actuators. A first thermomechanical micro actuator is disposed on the substrate in a manner known from prior art, being extended substantially in parallel with the surface of the substrate in response to a thermal stimulation, i.e. performing its positioning movement substantially in parallel with the surface. In accordance with the invention, the second thermomechanical micro actuator is, on the one hand, so configured that it is extended, in response to thermal stimulation, substantially in a direction orthogonal on the surface of the substrate, which means that it performs its positioning movement substantially in a direction normal on the substrate surface. On the other hand, the second thermomechanical micro actuator is so arranged that, in response to thermal stimulation, one section of the first thermomechanical micro actuator—in the extended state—reaches under one section of the second thermomechanical micro actuator. As the second thermomechanical micro actuator performs a positioning movement substantially in a direction orthogonal on the substrate surface, hence one section of the first thermomechanical micro actuator in an extended state is located between one section of the second thermomechanical micro actuator and the substrate surface so that this section of the first thermomechanical micro actuator will be clamped by the second thermomechanical micro actuator when the latter is switched off.
This arrangement of two thermomechanical micro actuators makes it hence possible to maintain the switching state (ON state) of the first thermomechanical micro actuator without power consumption. When the state is changed over from the neutral condition (OFF state) into the ON state, initially both thermomechanical micro actuators are energized, i.e. thermally stimulated, so that a first section of the first thermomechanical micro actuator moves underneath a second section of the second thermomechanical micro actuator. Then the second thermomechanical micro actuator is de-energized, thus clamping the first section of the first thermomechanical micro actuator. When the latter is subsequently de-energized, equally by interruption of the heat supply, it remains in the extended position because it is held in this position due to the clamping effect produced by the de-energized second thermomechanical micro actuator. This holding position becomes possible, on the one hand, due to the friction between the two micro actuators and, on the other hand, by the high restoring force with which the second thermal micro actuator assumes its neutral position. In this manner, the extended state of the first thermomechanical micro actuator is maintained without any further supply of energy, i.e. in a de-energized condition. The release from this holding position merely requires a short energy supply to the second thermomechanical micro actuator, which releases the holding position and cau

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