1. Technical Field
The present invention is related to an apparatus and method for moving a first object relative to a second object and holding them in a defined position. In particular, the present invention relates to a scanning system for micromechanical devices.
2. Description of the Prior Art
When an object is to be moved or driven with a defined precision, then a device that controls the object's position and movement is employed. Such a device is a scanner that includes an actuator, whereby various kinds of driving principles are known for those actuators. Well known are electromagnetic, electrostatic, superconducting, piezoelectric, ultrasonic, pneumatic, air-based, thermal expansion, bimetal, and shape-memory alloy actuators. Micro-actuators and the micro machines driven by them are expected to have wide varieties of applications in information technologies, in medical, bioengineering, optics, and robotics fields. For example, electromagnetic actuators are ubiquitous. They can be found in everything from a large train to the smallest time piece. However, even the smallest magnetic actuators are usually made with wound coils and magnetic materials.
In the European patent application publication no. EP 0 998 019 A1, currently owned by the present applicant, a magnetic scanning or positioning system with at least two degrees of freedom is described. The magnetic scanning or positioning system comprises a supporting base equipped with magnets, a movable platform equipped with at least two electrical coils, and suspension elements providing an elastic connection between the movable platform and the supporting base. The electrical coils are positioned flat on the movable platform, thereby forming an essentially flat arrangement with the movable platform. The scanning or positioning with at least two degrees of freedom can be used in the field of scanning probe microscopy or in the field of data storage or imaging.
Another example is known as an electrostatic actuator. European patent application publication no. EP 0 865 151 A2 describes such an electrostatic actuator. The electrostatic actuator comprises a first member and a second member. The first member has a first opposed surface that includes an array of driven electrodes with pitch and the second member has a second opposed surface including an array of drive electrodes. A support positions the first member adjacent the second member with the first opposed surface spaced apart from the second opposed surface by a spacing. The ratio of the spacing and the pitch should be less than eight, and is preferably less than 2.25. The support permits the first member to move relative to the second member, or vice versa. A voltage source establishes a spatially substantially alternating voltage pattern on the array of driven electrodes. An electrode control establishes a substantially alternating voltage pattern on the array of drive electrode, and selectively imposes a local disruption on the substantially alternating voltage pattern on the array of drive electrodes to move the movable one of the first member and the second member relative to the other.
European patent EP 0 071 066 B1, granted to the present applicant, discloses an electric traveling support. The traveling support comprises a piezoelectric plate resting on three legs whose bottom surface is insulated from the bench on which the support is to travel, by a dielectric. The piezoelectric plate can be caused to contract by means of an actuating voltage applied via sliders to top and bottom electrodes on the plate. By applying a voltage to the legs, these may be clamped selectively by electrostatic forces effective across the dielectric. Appropriate control of the actuating and clamping voltages causes the support to either move in a linear or rotary fashion.
All the aforementioned actuators and scanners need energy not only for movement but also for holding and positioning. Low power precise positioning of parts and devices become more and more important as (nano)micro-mechanics gains in importance. In particular in nano-mechanics on the bases of local probes where tips have to be positioned with nano-meter precision reliable scanners are missing. For piezo-scanners domain wall creep and for electromagnetic scanners thermal creep are unsolved problems. Additionally, present scanners consume energy for holding and restoring the last position. Furthermore for conventional scanners the energy needed for moving from position to position increases with increasing spring deformation.
It is therefore an object of the present invention to overcome the disadvantages of the prior art.
It is another object of the present invention to provide a scanner with integrated tracking and nearly zero power consumption for holding a position with high precision.