Contact-free thickness measuring method and device

A device for the contact-free measurement of a thickness of a workpiece having first and second surfaces which are opposite and plane-parallel to each other, said device comprising means for creating a single laser beam;

• means for splitting the laser beam into at least two sub-beams;
• means for directing each of the sub-beams to opposite sides of a reference plane;
• means for reflecting at least a portion of each of the sub-beams at the reference plane, said means for reflecting comprising a prism disposed on each side of the reference plane, each prism having a partially mirrored surface and a completely mirrored surface so that two portions are directed from each prism and each of said first and second surfaces of the workpiece which is disposed adjacent to the reference plane is struck by the two portions;
• means for causing each of the portions of the sub-beams to move periodically across the respective surface of the workpiece from an initial position and back, said means for causing comprises a piezo-electric beam deflector disposed between the means for providing a laser beam and the means for splitting so that all the sub-beams are deflected at the same speed and direction;
• a separate sensing means associated with each of the portions of the sub-beams for detecting a reflected beam arriving along a given path, said reflected beam being reflected by a scattering point on one of said first and second surfaces in a diffused fashion, said initial position of each portion and the given path for the associated sensing means intersecting at a point in the reference plane with the initial position forming an angle .alpha. with a normal of the reference plane and the given path forming an angle .beta. with the normal;
• means for measuring the time lapse from the initial position of each portion until the reflected beam is sensed and for converting each time lapse into a deflection angle .gamma.;
• means for calculating the distance d.sub.i of each scattering point from the reference plane according to ##EQU7## where i = 1,2,3 and 4, wherein .gamma..sub.i is the angle between the initial position and the position when the reflected beam of the given path is detected for a portion i, A.sub.i is the distance between the reference plane and the reflector i, .gamma..sub.i being positive when the angle of incidence of the portion increases and being negative when the angle decreases;
• and means for calculating the thickness d of the workpiece according to ##EQU8##

A method for the contact-free measurement of the thickness of a workpiece having first and second surfaces which are opposite and plane-parallel to each other, said workpiece being disposed adjacent a reference plane of a device having means for providing a laser beam, means for splitting the laser beam into at least two sub-beams, means for directing the sub-beams to opposite sides of the reference plane, means for reflecting at least a portion of each of the sub-beams at the reference plane and having at least one reflecting surface on each side of said reference plane so that each of said first and second surfaces of the workpiece is struck by at least one portion, means being disposed between the means for providing a laser beam and the means for splitting for causing each of the portions to move periodically across the respective surface of the workpiece from an initial position and back, and separate sensing means associated with each of the portions for detecting a beam reflected by a scattering point on one of said first and second surfaces arriving along a given path, each portion while in the initial position and the given path for the associated sensing means intersecting at a point in the reference plane with the initial position forming an angle .alpha. with a normal of the reference plane and the given path forming an angle .beta. with the normal, said method comprising deflecting the laser beam from an initial position;

• splitting the deflected laser beam;
• directing the sub-beams;
• creating two separate spaced portions of each sub-beam and reflecting the portions at the first and second surfaces of the workpiece, said deflecting causing each of said portions to be deflected from the initial position simultaneously and at the same rate, so that two portions moves along each of said first and second surfaces which reflect the respective portion in a diffused fashion as a reflected beam;
• sensing each reflected beam from a scattering point on the surface of the workpiece as the reflected beam assumes the given path;
• measuring the time lapse from the initial position of each portion until the reflected beam is sensed;
• converting each of the time lapses into a deflection angle .gamma.;
• calculating the distance d.sub.i of each scattering point from the reference plane according to ##EQU9## where i = 1,2,3 and 4 wherein .gamma..sub.i is the angle between the initial position and the position when a reflected beam of the given path is detected for the portion i, A.sub.i is the distance between the reference plane and the reflector i, .gamma..sub.i being positive when the angle of incidence of the portion increases and being negative when the angle decreases;
• and subsequently calculating the thickness d of the workpiece according to ##EQU10## so that a thickness of a workpiece, which is tilted in relation to the reference plane about two perpendicular axes which are parallel to the reference plane, can be determined.