Abstract: A capacitance probe is used by a coordinate measuring machine or machine tool to determine distances from the probe to the workpiece surface at various points over the surface. The probe is calibrated by moving it along a line, which is skewed to the surface. During this movement, a plurality of values of the capacitance and the corresponding values of the actual distance moved along the line are recorded. A datum value for the movement along the skewed line is also determined, which corresponds to a position at which the probe would touch the surface. The probe is calibrated without needing separate independent measurements of the distance from the probe to the surface. The workpiece surface is scanned using the thus-calibrate probe, in which different calibration values are used at different points on the surface, in order to account for the local shape of the surface.

Abstract: A laser diode has its frequency locked to the frequency of an absorption line of rubidium (water and oxides of nitrogen are also disclosed). The level of absorption, and hence the frequency relationship of the laser light with respect to the absorption line is detected by a photodetector. The absolute frequency of the laser light is guaranteed by initially adjusting the temperature of the diode until the frequency of the light is brought into coincidence with a first absorption line, subsequently maintaining the temperature at a constant level, and adjusting the drive current of the diode until the frequency of laser light achieves coincidence with an adjacent transition line. This ensures that the diode frequency is locked to the same absorption line each occasion the diode is switched on. Additionally, the change in drive current between coincidence with the two adjacent absorption lines is monitored as a further check that the correct transition line has been selected.

Abstract: An absolute interferometer has part of the beam paths making up its measuring and reference arms formed in a waveguide, and part formed in air. The part formed in the waveguide are common mode so that the path length difference is formed in air, thus minimizing inaccuracies in the measurements caused by temperature changes in the waveguide. Phase modulators in the waveguide enable interpolation of the fringe counts to be made to high resolution. The absolute interferometer may be combined with a tracking interferometer, and with air refractometers, all of which have parts of their measuring and reference arms in the waveguide in common mode and symmetrical with each other.

Abstract: A combined interferometer and refractometer includes two interferometers each of which uses a light beam produced from a common source which are split into measuring component beams and reference component beams. The measuring component beams are directed along parallel paths to an object and are reflected back from reflecting surfaces on the object which is so positioned as to produce a fixed path length difference between the beams. The reflected beams are re-combined with the reference component beams to produce output beams which pass to a detector system which derives an output signal from each. Changes in refractive index are determined from any difference in the two output signals, and the distance moved by the object is determined from any change in either one of the output signals or by summing them and dividing by two. Methods are described whereby the measurements of refractive index or of distance can be made absolute.

Abstract: A spot of a sample is illuminated by laser light. Raman scattered light is collimated in a parallel beam by a microscope objective, and analyzed by a dispersive or non-dispersive analyzer (such as a diffraction grating or filter). A lens then focuses the Raman scattered light onto a two-dimensional photodetector array in the form of a charge-coupled device (CCD). A confocal technique is described to eliminate light scattered from outside the focal plane of the objective. This may be done by binning together a few pixels of the CCD at the focal point of the lens, or by image processing techniques in a computer.

Abstract: A touch probe includes a stylus module (54) and a sensing module (52) to which the stylus module is releasably securable by a magnetic coupling. The sensing module comprises a strain sensitive load cell on which the stylus module is supported, and which senses strain in the stylus on contact with a surface. The stylus module provides for overtravel of the probe; a stylus-supporting member being biased into a kinematic rest position with respect to the casing of the stylus module. The biasing force in the stylus module is chosen with regard to the length and configuration of stylus. This modular system enables automated stylus changing without the need to adjust the biasing force on the stylus-supporting member when different lengths of styli are employed.

Abstract: A workpiece surface 30 is digitized by scanning it with the stylus 8 of a scanning probe 5. Digitized coordinate data for many points P1-P6 on the workpiece surface are subjected to a filtering algorithm, in order to remove redundant data when the surface is relatively flat or planar. Top and bottom tolerance vectors TV0,BV0 are defined, starting from a first point P1 and lying at a given tolerance h above and below a second point P2. Next, a direct vector DV1 is defined between the point P1 and a third point P3. If the vector DV1 lies outside the tolerance band between the vectors TV0 and BV0, then point P2 is deemed to be required and is not filtered out. Otherwise, the data for point P2 is deemed to be redundant and is rejected. In this case, new tolerance vectors TV1 and BV1 are now defined, starting from point P1 and passing within a tolerance h above and below point P3.

Abstract: An interferometric probe for measuring the distance to the surface of an object has a light source, for example, a super-luminescent diode, that produces a coherent light beam preferably such as to produce a speckle pattern in light reflected from the object. An interferometer includes a beam splitter that produces a reference beam directed towards a reference diffracting reflector and a measuring beam directed towards the surface of the object to be measured. The diffracting reflector produces a plurality of diffraction orders each of which are combined with portions of the light reflected from the surface to produce interference, which is detected by a detector system having a number of individual detectors equal to the number of diffracted orders of the reference beam that are used. Use of the diffracting reflector enables more of the light reflected from the object to be used in the detector and improves signal-to-noise ratio.

Abstract: An arm 12 for holding a tool-setting probe 14 in a machine tool is rotatable between an operative position and an inoperative position. The operative position is defined by elements 48,52 which form a stop against further rotary motion beyond the operative position. These elements 48,52 are arranged as a kinematic support, so that the operative position is defined in a precisely repeatable manner. Springs 40 urge the elements 48,52 together. When the arm is in the operative position, these springs are stretched by a repeatable amount, so that they provide a repeatable force, in order to increase the precision of the operative position.

Abstract: In a method of calibrating the measuring performance and apparatus for a machine, the conventional physical length bar is simulated by moving a retro-reflector to various positions along a track. A laser beam of an interferometer is aligned with the track using the retro-reflector at two extreme positions in order to define a measurement axis for the calibration. The retro-reflector has a part-spherical surface on its rear face which is centered on the nodal point of the retro-reflector. By contacting the reference surface with a probe on the machine at several points, the center of the sphere at the two positions of the retro-reflector can be calculated and hence the measurement axis is defined in the machine frame of reference.

Abstract: A sample placed under a microscope is illuminated by light from a laser beam. Raman scattered light is passed back via a dichroic filter to various optical components which analyse the Raman spectrum, and thence to a CCD detector. The optical components for analysing the Raman spectrum include tunable dielectric filters in a filter wheel; a Fabry-Perot etalon; and a diffraction grating. These various components may be swapped into the optical path as desired, for example using movable mirrors, enabling the apparatus to be used very flexibly for a variety of different analysis procedures. Various novel analysis methods are also described.

Abstract: A touch trigger probe incorporates piezoelectric sensors 50, whose outputs are processed by an interface circuit. The interface circuit discriminates between signals generated from the piezoelectric sensors 50 as a result of machine vibration and those generated as a result of a genuine measurement event, by the use of a timing circuit 90. The timing circuit 90 compares the time intervals (t.sub.1 -t.sub.2);(t.sub.2 -t.sub.3) between attainment of first 1.sub.1 and second 1.sub.2, and second 1.sub.2 and third 1.sub.3 output signal levels from the sensor 50, and upon the basis of this comparison validates (or rejects) measurements made with the probe. Additionally, the interface determines whether measurements made with the probe are taken upon the basis of outputs generated by the sensors 50 due to a shock wave in the stylus 24 of the probe, or as a result of strain in the stylus 24; as an alternative, measurements may be made only on the basis of strain.

Abstract: Apparatus for and a method of scanning a workpiece are in the form of a retrofit package which provides a scanning capability for a machine tool which would otherwise have none. The basic elements of the package are a scanning probe, a computer, an interface between the probe and the computer, and a link between the computer and the RS232 (or other serial port) of the machine controller for communicating between the two. According to the method, the computer signals the machine control system to drive to a target position and stop, reads the probe outputs when the machine has stopped, calculates a new target position and signals it to the machine control system. To ensure that the machine has stopped the computer calculates time intervals based on its knowledge of the machine velocity, or motion signals based on a motion sensor or the probe outputs and only latches the probe readings when the time has expired or when the probe/motion sensor indicates that motion has ceased.

Abstract: A method of determining surface contour of diffusely reflecting objects is realized by interferometric comparison of beams reflected from a reference mirror and from an object (11), by changing the optical path length of the object beam, by focusing the object beam onto a plane corresponding to the zero path length difference between the beams being compared interferometrically, and by measuring said variation of the optical path length from an initial value up to a moment when appears an interference pattern displaying maximum contrast.

Abstract: An analogue probe 100 includes a fixed structure 110 and a stylus supporting member 112 suspended relative to the fixed structure 110 by three serially connected pairs of leaf springs 114,116,118. Displacement of the supporting member 112 relative to the fixed structure 110 is transduced by three opto-electronic scale and readhead transducers 136,144;138,146;140,148. The distorting effect of bending moments applied to the tip 130 of the stylus 128 upon leaf springs 114,118 is counteracted by an increased spacing between upper ends of leaf springs of a given pair, relative to the spacing between leaf springs at their lower ends; the resulting arrangement forming a trapezium as opposed to a rectangle. This enables longer styli to be employed before distortion of the leaf springs causes failure of the opto-electronic transducers due to unwanted tilting of the supporting member 112.

Abstract: A connecting device for connecting a shank 16 to a measuring probe 18 is disclosed, to enable the probe 18 to be incorporated on a machine tool for the purpose of tracing a contour of a model. The device includes first and second parts (20,22) connected to the shank and the probe respectively, retained together by a connecting bolt 50 which is spring-loaded by means of Belville washers 56. An arm 60 extends from the second part to engage the housing 14 of the spindle 10, and thereby prevent rotation of the spindle shaft 12. In the event of accidental spindle start-up the two parts 20,22 may rotate relative to each other (the shank rotating with the shaft 12); a thrust bearing 42 enabling sliding of the two parts.

Abstract: A touch trigger probe for a coordinate measuring machine or machine tool has a stylus (14), which is biased into a rest position. The stylus has two independent supports, provided within a housing (10). In the embodiment of FIG. 1, the first support comprises a skirt (18) of a stylus holder (12), which is axially constrained on a surface (20) of the housing (10). The second support comprises a kinematic arrangement of cylinders (34) and balls (36), together with a planar spring (30), which together provide lateral constraint. The first support is biased by a much lighter force than the second support, so that its friction is very low. This reduces the lobing and hysteresis of the stylus movement, and thereby increases the accuracy of the probe.

Abstract: A coordinate positioning machine is equipped with either an optical probe or a contact measuring probe. Movement of the head of the machine to enable the probe to scan an unknown surface is controlled by predicting the position of a subsequent point to which the head of the machine is to be driven upon the basis of three most recently measured points, P.sub.1, P.sub.2, P.sub.3. The prediction of the subsequent point P.sub.4 is performed by machine control in real time.

Abstract: A touch probe comprises a stylus-supporting member kinematically supported with respect to a housing at six points of contact between the stylus-supporting member and the housing. At each of these points of contact a conducting surface on the stylus-supporting member abuts a conducting surface on the housing. Each of the contacts are included in an electrical circuit. The conducting material of each of the conducting surfaces comprises a material having a resistivity of less than 8 .mu..OMEGA.cm and a melting voltage of at least 0.7 volts. A material having these properties is less susceptible to physical degradation than prior art materials used in such a probe. In a preferred embodiment the conducting material of each of the conducting surfaces is made of pure tungsten.

Abstract: A laser interferometer uses an acousto-optically modulated laser (100) to produce a pair of orthogonally polarized frequency-shifted beams. The beams are passed down a monomode, polarization preserving optical fiber (110) in order to transmit the beams to a cavity (148). The beams are separated at polarizing beam splitter (128) and directed down measuring arm (130) and reference arm (132) of an interferometer. The beat frequency between the reflected beams is detected at photo-detector (146) which outputs a measuring signal (152). This beat frequency is compared to the beat frequency of the beams before entering the interferometer, which is derived by providing a semisilvered mirror (114) and interfering polaroid (116) in the path of the beams up-beam of the interferometer to produce a reference signal (126). The measuring and reference signals are compared to determine the movement of the measuring arm of the interferometer.