Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Patent
1998-11-12
2000-05-02
Manuel, George
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
A61B 310
Patent
active
060564024
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention is an optomechanical device for the ophthalmologist or optician with which the test glasses can be varied in the course of the subjective adjustment of correction glasses.
STATE OF TECHNOLOGY
In the course of the subjective adjustment of correction glasses (spectacles or contact lenses) in general nowadays what is known as a "phoropter" is used for presenting the test glasses. In this connection, in state-of-the-art devices (e.g. U.S. Pat. No. 4,500,180, DE2901459) spherical and cylindrical lenses for each eye are usually arranged on lens discs (revolving wheels). Other versions (e.g. DE3331799) use a pair of Stokes' lenses, as they have been known since the mid-nineteenth century, as cylinder glasses. The mechanical construction with these Stokes' lenses is considerably simpler as only two lenses all told are required for all cylinder strengths and axes, however, rather high demands are made on the setting accuracy for the rotation of both lenses against one another and the link between the relative angle and the resultant cylinder strength is not linear. A pair of Stokes' lenses can therefore only be implemented in practice in a phoropter together with a computer which calculates the relative angle required in each step for the cylinder strength desired and which controls an electric motor drive for each lens ensuring an adequate setting accuracy.
In general, stepper motors meeting state-of-the-art requirements are usually used nowadays for phoropter drives, either for the revolving wheels with or without planetary gears, or for Stokes' lenses. These stepper motors then drive the mountings of the optical components through appropriate mechanical gear reductions meaning in most cases not inconsiderable complexity with corresponding possible faults and production costs. In addition, the mechanical dimensions of such phoropters are quite large. Recently, phoropters have also become available on the market (DE4425443) which, instead of the stepper motor drives mentioned, use electrostrictive (in general piezoelectric) stepper micromotors. With these drives, the mechanical complexity is markedly less and the positioning accuracy (number of steps per rotation) is greater too. Admittedly, these drives usually display a certain amount of "slippage" so that additional means have to be taken for the continuous position measurement. As well as that, very tight production tolerances must be met which additionally increases the costs.
The task of this present invention is to make available a phoropter with an electromechanical drive which combines a very high setting accuracy with very small mechanical dimensions and little production complexity.
SHORT DESCRIPTION OF THE INVENTION
The task is solved in the invention in accordance with the characteristic features of claim 1.
In order to move the rotating components (revolving wheels or Stokes' lenses, hereinafter called "rotors" while the stationary parts of the drive are called "stators" as a whole) an electromagnetic direct drive is used, as is known in another connection, for example from U.S. Pat. No. 4,596,449, which is implemented in the following manner. On a circumference periphery of each rotor n magnetisable components of the same kind (hereinafter called "yokes") are located at constant angle distances .alpha., fastened in non-magnetisable surroundings. Directly opposite the same on a circumference periphery of the stator are located m electromagnets of the same kind also at constant angle distances .beta.. The centre-points of the two said circumferences lie on the axis of rotation and the rest of the geometry is arranged in such a manner that the electromagnets and yokes stand opposite to each other separated only by a small air gap. The angle distances .alpha. and .beta. are chosen in such a manner that a "vernier arrangement" results for the positions of the yokes and electromagnets with respect to one another, that means that for the differential angle .gamma.=.vertline..alpha.-.beta..vertline. either m.multidot..ga
REFERENCES:
patent: 5739959 (1998-04-01), Quaglia
patent: 5914772 (1999-06-01), Dyer
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