Abstract:
A device has a first object and a second object each with an at least partially parallel surface facing the other. The device also has an oscillator for creating an oscillation of a medium between the first and second objects to generate an air bearing between the first and second objects. Relative movement between the first and second objects is permitted via this configuration. A method for creating an air bearing between two at least partially parallel surfaces facing each other is also provided.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates in general to an improved device and method for creating an air bearing. More particularly, the present invention relates to movements with reduced friction between objects. 
     2. Description of the Prior Art 
     The movement of objects is bind to loss of energy because of friction. Friction is a force that opposes the motion of an object when the object is in contact with another object or surface. Friction results from two surfaces rubbing against each other or moving relative to one another. It can hinder the motion of an object or prevent an object from moving at all. The strength of frictional force depends on the nature of the surfaces that are in contact and the force pushing them together. This force is usually related to the weight of the object or objects. Usually, the friction between the moving objects of a device, e.g. an engine, turns energy into heat, reducing the device&#39;s efficiency. Friction also makes it difficult to slide a heavy object. Two surfaces in contact also tend to attract one another at the molecular level, forming chemical or physical bonds. These bonds can prevent an object from moving, even when it is pushed. If an object is in motion, these bonds form and release. Making and breaking the bonds takes energy away from the motion of the object. 
     The normal force is the force the object exerts perpendicular to the surface. In the case of a level surface, the normal force is equal to the weight of the object. If the surface is inclined, only a fraction of the object&#39;s weight pushes directly into the surface, so the normal force is less than the object&#39;s weight. 
     Different kinds of motion give rise to different types of friction between objects, for example static friction, sliding friction, also called kinetic friction, or rolling friction. While friction allows to convert one form of motion to another, it also converts some energy into heat, noise, and wear and tear on material. Losing energy to these effects often reduces the efficiency of a machine. 
     Reducing the amount of friction between objects increases the efficiency of the movement. Less friction means less energy lost to heat, noise, and wearing down of material. 
     Several methods for reducing friction are known. One method involves reducing the roughness of the surfaces in contact. Applying a lubricant to a surface can also reduce friction. Common examples of lubricants are oil and grease. They reduce friction by minimizing the contact between rough surfaces. The lubricant&#39;s particles slide easily against each other and cause far less friction than would occur between the surfaces. 
     A more efficient way to move an object and to reduce friction is to have an air cushion. Air cushions have a long history. Known are, for example, air-cushion vehicles, also called hovercrafts, crafts that operates above the surface of water or land. Such a vehicle is supported on a cushion of air. The air cushion is provided by a large fan that pushes air downward within a flexible skirt attached to the perimeter of the vehicle. The skirt maintains the cushion by restraining the air. It makes the vehicle appear to be operating only a few inches above the surface. The vehicle is moved forward by propellers mounted above the vehicle or by control of the air exhaust through small openings around the skirt. 
     In magnetic recording, a head is sliding on an air cushion over a disk in order to avoid the contact between the head and the disk which may lead to wear. This is achieved by the specific construction of the head&#39;s shape. Moreover, several production or assembly lines using airflows or air bearing conveyers for the transport of materials or goods, e.g. wafer. In mechanical engineering compressed air is blown into bearings, so called air bearings, to achieve reduced friction during rotations. 
     The most of the aforementioned techniques use a flow of air to generate an air cushion or air bearing. This flow might be generated by a fan. In the micromechanical world, systems allowing reduced friction are nearly unknown. This calls for innovative solutions, since it becomes crucial in the near future, when spinning disks, for example, get smaller and smaller entering the micromechanical regime. Thus, it is an object of the present invention to provide a nearly frictionless system for moving objects relative to each other. 
     SUMMARY AND ADVANTAGES OF THE INVENTION 
     In order to achieve the objectives of the present invention, a device comprises a first object and a second object each having an at least partially parallel surface facing each other. The device further comprises an oscillator for creating an oscillation of a medium between the first and second objects to generate an air bearing between the first and second object. Thereby relative movement between the first and second objects is permitted. 
     A method for creating an air bearing between the first object and the second object each having an at least partially or to some extent parallel surface facing each other is also provided. The method comprising the step of oscillating a medium between the first and second surfaces to generate an air bearing between the first and second objects. Using the device or method, a nearly frictionless movement between the surfaces of the objects can be achieved. Therefore, no lubrication is necessary at all. The invention is particularly well suited for micromechanical applications but is not restricted to them. 
     In one aspect of the present invention, the device comprises at least a spacer between the first and second object. This is advantageously because then the first object is separated from the second object and the creation of the air bearing can be initiated more easily. When the spacer comprises a cantilever having a contact area with one of the first or second objects or the spacer is a foot, then the advantage occurs that the distance between the first and second object can be exactly defined. This may play a role when several objects are placed on the air bearing. The cantilever can have a tip, then the advantage occurs that the contact area is very small and the forces between the tip and the first or second object can be overcome easily without much power. It is advantageously if many several objects, e.g. robots, have different surfaces, shapes, or weights such that each object starts its movement at a defined resonant frequency. By doing so, individual control of a lot of objects is achievable. 
     The oscillator for the oscillation of the medium between the first and second object might comprise piezoelectric, capacitance, electromagnetic, or ultrasonic elements. By using the listed elements, the stimulation of the medium to oscillate can be generated efficiently by well-understood techniques. The medium in-between the first and second objects may comprise air, a gas, or a mixture thereof, but also a liquid or a thin liquid might be advantageous for some applications. 
     It should be noted that not only the medium can be oscillated but also the first and second objects or even a combination thereof. With air bearing is meant that not necessarily air between the first and second object permits relative movement, but also a gas or a liquid or any other suitable medium can be applied in order to reduce the friction between the objects. 
     If one of the first and second objects comprises an imbalance or unbalance, than an unbalanced movement of one of the first and second objects can be achieved. If the object having the unbalanced movement is encircled by a wall or a tube, than the advantage occurs that this object adjusts itself to a constant rotation. When the first object has a recess for reception of the second object, then the advantage occurs that the second object adjusts or centers itself by the air vibrations. If the second object is a disk or a wheel and its motion is activated by capacitance, magnetic or airflow means, then a high speed motor can be provided. 
     If the first object encircles at least partly the second object, then the advantage occurs that the device with the first and second object can be operated at different angles. One of the first and second objects is a moving part, also referred to as moving object. Therefore, the moving object can be everything which is useful to move, for example a disk, a tool, a container, a plate, a write/read unit, or a robot. 
     If the moving object is rotating it appears advantageous if a spindle guides the moving object. Owing the moving object holds its defined position. Also possible is a guide element. For example, a wall or a tube might be applicable that oscillates at its radius. It is also possible to arrange several guide wheels or the like at the circumference of the moving object in order to guide the moving object on a predefined position or place. 
     The movement of the moving object, e.g. in the x- and y-direction, can be achieved by driving means such as electromagnetic, electrostatic or capacitance elements. For that, coils, electric and dielectric materials can be arranged properly as it is well known by a skilled person. Also possible and easy to implement are airflow means, like jets or fans. 
     It is favorable that the movement of the moving object by the driving means can be initiated by a single pulse stimulation, because then a longer distance can be covered whilst by periodic stimulation short distances can be covered. Furthermore, a stimulation in different directions can be applied, then the advantage occurs that a rotation of the moving object is achievable. By doing so, a precise motor can be created. 
     It proves as favorable for the nearly frictionless movement of the moving object, that the moving object only moves when a defined distance to the other object is provided. The air bearing between the first and second object can have different resonant frequencies. This is advantageous, because then several moving objects can be driven at different resonant frequencies which means at different times. An individual control of each second object is therewith possible. The thickness of the air bearing between the first and second objects can be varied by adapting the pressure between the objects. This permits a fine adjustment in the z-direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are described in detail below, by way of example only, with reference to the following schematic drawings. The drawings are provided for illustrative purpose only and do not necessarily represent practical examples of the present invention to scale. 
     FIG. 1 shows a schematic illustration of a first embodiment according to the present invention. 
     FIG. 2 shows a second embodiment according to the present invention. 
     FIG. 3 a  shows a third embodiment according to the present invention. 
     FIG. 3 b  shows a forth embodiment according to the present invention. 
     FIG. 4 shows a fifth embodiment according to the present invention. 
     FIG. 5 shows a top view of the embodiment shown in FIG.  4 . 
     FIG. 6 shows a top view of a further embodiment comprising sliders. 
     FIG. 7 shows a schematic illustration of a guided disk. 
     FIG. 8 shows a schematic illustration of an embodiment with several moving objects. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following, the various exemplary embodiments of the invention are described. Although the present invention is applicable in a broad variety of mechanical applications it will be described with the focus put on a micromechanical application. 
     FIG. 1 shows a schematic illustration of a first embodiment. A nearly frictionless device  1  comprises a first object  10  that here is a substrate  10  and a second object  20  that here is a spinning disk  20 . The substrate  10  has a first surface  11  and the spinning disk  20  has a second surface  21 , whereby the surfaces  11 ,  21  facing each other. The substrate  10  is arranged on an oscillator  30  that here is a piezoelectric oscillator  30 . The spinning disk  20  is separated from the substrate  10  by a plurality of spacers  2 . Here, the spacers  2  are cantilevers with a tip mounted to the substrate  10 . The spacers  2  ease the lift off of the spinning disk  20 . On top of the spinning disk is a spindle  50  arranged in order to apply a small force to the center of the spinning disk  20 . The spindle  50  is mounted on a spring  52 , that is deformed when the spinning disk  20  lifts off. 
     The spinning disk  20  lifts off when the medium, e.g. air, between the spinning disk  20  and the substrate  10  oscillates in such a way that an air bearing  40  occurs that has a thickness and the pressure such that the spinning disk glides on it. The piezoelectric oscillator  30  oscillates the substrate  10  in a direction perpendicular to the first surface  11 . This is shown by an arrow and the dotted lines indicating the edges of the oscillating substrate  10 . 
     The air in the gap, i.e. the air in-between the surfaces  11 ,  21  of the substrate  10  and the spinning disk  20  is actuating as a hard spring, because the air cannot come out on the side of the gab. This works around resonant frequency and through the air there are nearly no linear effects. 
     A relative movement between the substrate  10  and the spinning disk  20  can be achieved by several driving means or techniques. The movement, for example, can be generated by a capacitor, an electromagnet, an electrostatic element, or an airflow. The rotation of the spinning disk  20  can be initiated by any one of the aforementioned means or techniques. As a driving means is shown an airflow generator or fan  22  to create an airflow which drives the spinning disk  20 . 
     FIG. 2 shows a second embodiment, whereby the same reference numerals are used to denote the same or like parts. The device in FIG. 2 comprises the substrate  10  on the piezoelectric oscillator  30  separated from the spinning disk  20  by cantilevers  2 . On top of the spinning disk  20  is a plate  60  arranged such that the spinning disk  20  is sandwiched between the substrate  10  and the plate  60 . Both  10 ,  60  are equipped with cantilevers  2 ,  62 . An axis  54  is arranged at the center of the spinning disk  20  to hold the spinning disk  20  at its position. Here, the plate  60 , equipped with the cantilevers  62 , is used to transform a stepwise rotation as a kind of “linear” motion into a continuous rotation. This represents a motor. 
     FIG. 3 a  shows a third embodiment in cross-sectional view where the spinning disk  20  is positioned and fixed in a three dimensional nearly frictionless setup. The same reference numerals are used to denote the same or like parts. The substrate  10  has a recess  12  for the reception of the spinning disk  20 . Here, the spinning disk  20  has an enlarged surface to achieve a better centering. Also sliders mounted on or attached to the spinning disk  20  would improve the centering. For the sake of simplicity, such sliders are not shown in the figure. Moreover, a capacitor structure  24 , short capacitor  24  is arranged on the substrate  10  and the spinning disk  20 . The spinning disk  20  is activated to rotate by the capacitor structure  24  or other suitable driving means. If the substrate  10  is activated by oscillation through the piezoelectric oscillator  30  and the air bearing  40  is generated, the spinning disk  20  is lifted off and centered by the air vibration. In the third dimension, i.e. in the z-direction, the disk might be trapped by another oscillating disk like shown in FIG. 2, resulting in a three dimensional air cushion. A nearly frictionless high speed motor can be provided. 
     FIG. 3 b  shows a forth embodiment which is similar to the embodiment described with reference to FIG. 3 a . The same reference numerals are used to denote the same or like parts. FIG. 3 b  shows a nearly frictionless bearing with a rotating hard disk  20 , whereby additional parts can be mounted on the hard disk  20  or the substrate  10 . During gliding on the air bearing  40  the hard disk  20  centers itself. 
     FIGS. 4 and 5 show a fifth embodiment in cross-sectional and top view where the spinning disk  20  is surrounded by three guide elements  60 . The same reference numerals are used to denote the same or like parts, whereby the substrate  10  has no recess. Each of the three guide elements  60  can be seen as a wall oscillating perpendicular to the direction of the oscillator  30 . Such a wall can be made of piezoelectric material. The oscillation of the guide elements  60  into the direction of the center of the spinning disk  20  additionally supports the air bearing and thereby the gliding of the spinning disk  20 . The oscillations are indicated by the arrows and the dotted lines indicating the edges of the oscillating substrate  10  and guide elements  60 , respectively. The rotation of the spinning disk  20  is initiated by electromagnetic elements, which for the sake of clarity are not shown in the figure. 
     FIG. 6 shows a top view of a further embodiment comprising sliders  80 . The spinning disk  20  is arranged within a tube  70 , whereby this tube has three sliders  80  arranged at its inner side towards the circumference of the spinning disk  20 . The sliders  80  are formed such that the medium between the tube  70  and the spinning disk  20  is compressed in a defined way. The sliders  80  could be arranged as well as on the spinning disk  20 . It might be additional advantageous if the radius of the tube  70  varies by oscillation, as described with reference to FIGS. 4 and 5. Furthermore, the spinning disk  20  might have an imbalance or unbalance. 
     FIG. 7 shows a schematic illustration of a guided spinning disk  20  by guide elements  60 . Here, three wheels  65  are arranged at the circumference of the spinning disk  20 . Each wheel  65  is fixed at its center. The spinning disk is guided on its outside by the wheels  65  instead of the center. 
     Referring still to FIG. 8, where a schematic illustration of an embodiment with several moving objects  20  is shown. The moving objects  20  are micro-robots  20  which can move individually in x- and y-directions, as indicated by the arrows, on the oscillating substrate  1 . The individual movement is achieved by the different resonant frequencies of each micro-robot  20 . An individual control of a lot of micro-robots  20  can be provided. As shown, the micro-robots  20  have different shapes. They can also have different weights or spacers  2 . The spacers  2 , e.g. cantilevers, can be on the side of the substrate  1  or on the side of each micro-robot  20  depending on the application. 
     By using the air bearing  40 , a very precise distance control between the first object  10  and the second object  20  is provided. The working range in an experiment was around 2-4 micrometer in z-direction. The resonant frequency was around 8 kHz, stable, and reproducible. A nearly frictionless movement in the z-direction and also in the x- and y-directions by activating a movement in these directions can be guaranteed. The motion of the moving object  20  in x- and y-directions can be linear as well as rotational by actuators or driving means  22 ,  24 . This driving means  22 ,  24  can be external or internal. Internal means, the cantilevers by themselves can initiate the movement of the direction by special actuation. The distance of move can be defined by a periodic stimulation of a single pulse. Moreover, the movement in the z-direction can be phase locked to the z actuation. That means, nearly frictionless movement in x- and y-direction is only possible if a defined distance between the first object  10  and the second object  20  is provided. The nearly frictionless movement in x- and y-direction can be achieved in x/y resonant or non resonant mode. 
     Any disclosed embodiment may be combined with one or several of the other embodiments shown and/or described. This is also possible for one or more features of the embodiments.