Surface sensing device with optical sensor

Abstract

A surface sensing device for use in position determining apparatus has an elongate stylus ( 74 ) with a tip ( 82 ) for scanning the surface of a workpiece to be measured. Lateral displacements of the stylus tip are detected by a light beam which passes along the stylus from a light source ( 66 ) to a retroreflector ( 78 ). This reflects the beam back via a beamsplitter ( 70 ) to a position sensitive detector ( 76 ). The stylus is mounted for longitudinal displacement on a carriage ( 72 ). The longitudinal displacement is measured by another light beam projected by the beamsplitter ( 70 ) onto a second position sensitive detector ( 84 ).

The invention claimed is: 
     
       1. A surface sensing device for use in position determining apparatus, comprising:
 an elongate stylus having a workpiece-contacting stylus tip; 
 an optical element at or near or connected to the tip so as to be subjected to lateral displacements of the tip; 
 an optical transducer system which projects a light beam along the stylus between a the between the optical element and a detector, thereby to measure said lateral displacements of the tip; 
 a mounting for the stylus the of the surface sensing device which enables only longitudinal displacement and bending of the stylus and constrains other movements thereof, the mounting for the stylus disposed within a housing of the surface sensing device, wherein the longitudinal displacement of the stylus is at the mounting for the stylus within the housing of the surface sensing device; and 
 a displacement measurement transducer arranged to measure said longitudinal displacement of the stylus. 
 
     
     
       2. A surface sensing device according to  claim 1 , wherein the stylus is bendable to permit said lateral displacements of the tip. 
     
     
       3. A surface sensing device according to  claim 1 , wherein the displacement measurement transducer arranged to measure longitudinal displacement comprises a further light beam projected onto a further detector. 
     
     
       4. A surface sensing device according to  claim 3 , including a beamsplitter which derives both light beams from a common light source. 
     
     
       5. A surface sensing device according to  claim 1 , wherein the stylus is mounted on a longitudinally movable carriage. 
     
     
       6. A surface sensing device according to  claim 5 , wherein the carriage is mounted for longitudinal movement on a pair of parallel leaf springs or diaphragms. 
     
     
       7. A surface sensing device according to  claim 1 , wherein the stylus has two portions, one of which is stiffer than the other. 
     
     
       8. A surface sensing device according to  claim 1 , comprising a probe, wherein the stylus is exchangeably attached to the probe. 
     
     
       9. A surface sensing device according to  claim 8 , wherein the probe comprises a longitudinally movable carriage, to which the stylus is exchangeably attached, and wherein said displacement measurement transducer is arranged to measure longitudinal displacement of the carriage. 
     
     
       10. A surface sensing device according to  claim 8 , wherein the exchangeable stylus adjusts the gain of the transducer system which measures the lateral displacements of the stylus tip. 
     
     
       11. A surface sensing device for use in position determining apparatus, comprising:
 an elongate stylus having a workpiece-sensing stylus tip; 
 the stylus having a relatively flexible portion permitting bending of the stylus and a relatively stiff portion, the relatively stiff portion being closer to the tip than the relatively flexible portion: 
 said tip being subjected to lateral displacements caused by bending of the stylus; 
 a transducer system which measures lateral displacements of the tip, including those caused by said bending of the stylus; 
 a mounting for the stylus in the surface sensing device which enables longitudinal displacement of the stylus, the mounting for the stylus disposed within a housing of the surface sensing device, wherein the longitudinal displacement of the stylus is at the mounting for the stylus within the housing of the surface sensing device; and 
 a displacement measurement transducer arranged to measure said longitudinal displacement of the stylus. 
 
     
     
       12. A surface sensing device according to  claim 11 , wherein the transducer system is optical. 
     
     
       13. A surface sensing device according to  claim 12 , wherein the transducer system includes an optical element at or near or connected to the tip so as to be subjected to the lateral displacements of the tip, and a detector, and wherein the transducer system projects a light beam between the optical element and the detector. 
     
     
       14. A surface sensing device according to  claim 11 , wherein the displacement measurement transducer for measuring longitudinal displacement comprises a detector, and projects a light beam onto the detector. 
     
     
       15. A surface sensing device according to  claim 7 , comprising a probe, wherein the probe comprises a longitudinally movable carriage, to which the stylus is exchangeably attached, and wherein said displacement measurement transducer is arranged to measure longitudinal displacement of the carriage. 
     
     
       16. A surface sensing device according to  claim 11 , comprising a probe, wherein the stylus is exchangeably attached to the probe. 
     
     
       17. A surface sensing device according to  claim 16 , wherein the exchangeable stylus adjusts the gain of the transducer system which measures the lateral displacements of the stylus tip. 
     
     
       18. A surface sensing device for use in position determining apparatus, comprising:
 a probe housing;   a longitudinally movable carriage mounted within the probe housing;   an elongate stylus having a workpiece-sensing stylus tip;   the longitudinally movable carriage providing a mounting for the stylus, which enables longitudinal displacement of the stylus at said mounting for the stylus within the housing;   the stylus being exchangeably attachable to and detachable from the carriage;   a displacement measurement transducer in the probe housing arranged to measure said longitudinal displacement;   said stylus tip being subject to lateral displacements;   a transducer system located at least partially in the exchangeable stylus, and arranged to measure said lateral displacements of the tip.   
     
     
       19. A surface sensing device according to claim 18, wherein the exchangeable elongate stylus is bendable to permit said lateral displacements of the stylus tip. 
     
     
       20. A surface sensing device according to claim 18, wherein the transducer system for measuring the lateral displacements of the stylus tip includes a detector and projects a light beam along the exchangeable elongate stylus to the detector. 
     
     
       21. A surface sensing device according to claim 20, wherein the transducer system for measuring the lateral displacements of the stylus tip comprises an optical element at or near or connected to the stylus tip so as to be subjected to lateral displacements of the stylus tip; and the light beam is projected between the optical element and the detector of the transducer system. 
     
     
       22. A surface sensing device according to claim 20, wherein the detector of the transducer system for measuring the lateral displacements of the stylus tip is located in the probe housing. 
     
     
       23. A surface sensing device according to claim 20, wherein the displacement measurement transducer in the probe housing for measuring said longitudinal displacements of the exchangeable stylus comprises a further light beam projected onto a further detector. 
     
     
       24. A surface sensing device according to claim 23, including a beamsplitter which derives both light beams from a common light source. 
     
     
       25. A surface sensing device according to claim 18, wherein the displacement measurement transducer in the probe housing for measuring said longitudinal displacements of the exchangeable stylus comprises a light beam projected onto a detector. 
     
     
       26. A surface sensing device according to claim 18, wherein the carriage is mounted for longitudinal movement on a pair of parallel leaf springs or diaphragms. 
     
     
       27. A surface sensing device according to claim 18, wherein the exchangeable stylus is configured to adjust the gain of the transducer system arranged to measure the lateral displacements of the stylus tip. 
     
     
       28. A surface sensing device according to claim 27, configured such that the stylus is exchangeable for alternative styli by automatic stylus changing apparatus. 
     
     
       29. A surface sensing device according to claim 18, wherein the stylus is exchangeably attachable to and detachable from the carriage via a kinematic mount. 
     
     
       30. A surface sensing device according to claim 29, wherein the stylus is magnetically attracted into the kinematic mount. 
     
     
       31. A surface sensing device according to claim 18, configured such that the stylus is exchangeable for alternative styli by automatic stylus changing apparatus.