EP0179083A1 - Sonde de mesure de pieces a usiner - Google Patents

Sonde de mesure de pieces a usiner

Info

Publication number
EP0179083A1
EP0179083A1 EP19850901523 EP85901523A EP0179083A1 EP 0179083 A1 EP0179083 A1 EP 0179083A1 EP 19850901523 EP19850901523 EP 19850901523 EP 85901523 A EP85901523 A EP 85901523A EP 0179083 A1 EP0179083 A1 EP 0179083A1
Authority
EP
European Patent Office
Prior art keywords
displacement
probe
stylus
output
base
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19850901523
Other languages
German (de)
English (en)
Inventor
Michael John Rogers
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Renishaw PLC
Original Assignee
Renishaw PLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Renishaw PLC filed Critical Renishaw PLC
Publication of EP0179083A1 publication Critical patent/EP0179083A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/004—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring coordinates of points
    • G01B7/008—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring coordinates of points using coordinate measuring machines
    • G01B7/012—Contact-making feeler heads therefor

Definitions

  • This invention relates to a probe for measuring the dimensions of workpieces.
  • the measuring devices of the machine are used to move the probe to a known demanded position relative to the surface to be measured, and the probe itself has a shortrange measuring device whereby to determine the amount by which the actual position of the surface differs from the demanded position.
  • a known type of proportional probe (British Patent No. 1,573,447) has a base, a stylus, resilient means for supporting the stylus on the base for displacement relative thereto between a rest position and a displaced position, means defining a pair of orthogonal coordinate axes, and means for measuring said displacement in terms of component outputs defining respective coordinate components of the displacement.
  • This has the advantage that the same probe can be used for either purpose. Also, inasmuch as the measuring probe can be constructed to have high accuracy, such accuracy would also be available in the trigger mode for determining the instant at which the step signal is generated.
  • trigger probes there is a difficulty in accurately relating the instant at which the stylus engages the workpiece to the instant at which the step signal is produced.
  • the unavoidable displacement of the stylus between these two events (the "pre-travel" of the stylus) is not always uniform for all conditions of operation.
  • the pre-travel may be different for different directions of displacement of the stylus relative to the base. Since the measurement by the measuring devices of the machine is carried out while the probe is in motion, then, for a given speed of that motion, any variation in pre-travel results in a variation of the measurement.
  • the improvement made by the last-mentioned trigger probe was not sufficient for increasing demands for accuracy.
  • the problem was that it is difficult to make the generally annular seat such as to provide the same seating accuracy all round the annulus, i.e. in some places the seat surface was higher than in others. Also there is a difficulty in ensuring that the transducer is positioned at the centre of the annulus. As a result, when the stylus was tilted, the pre-travel differed for different direction of tilt. Even if the seat was made in the form of a circular knife edge (British Patent No. 2,094,478) it was difficult to ensure with sufficient accuracy that the height of this knife edge was uniform all round its circumference and that the transducer was at the centre thereof.
  • the problem may be stated as follows.
  • the step signal occurs when the moveable part of the transducer has a given position relative to the fixed part. Due to manufacturing tolerances of mechanical components there arises variation in pre-travel. This is equivalent to the rest position of the stylus being different for different direction of displacement, a situation which would obviously falsify the measurement.
  • a probe for measuring the dimensions of workpieces comprising a base, a stylus having a free end whereby, in use, to engage a workpiece, support means for supporting the stylus on the base for displacement relative thereto between a rest position and a displaced position, means defining a pair of orthogonal coordinate axes, and means for determining a said displacement in terms of coordinate outputs defining respective coordinate components of the displacement: charaterised by combining means for combining said outputs into a resultant output being a function of said displacement, and threshold means for generating a step signal when said resultant output crosses a given value during a said displarement.
  • the step signal occurs at a value of said resultant output which is constant for all directions of said displacement and is the radius (the "trigger radius") of a circle or, if three components are used, of a sphere whose centre can be used to define the rest position of the stylus.
  • Said given value ⁇ f the resultant output may, for example, be 1 volt calibrated to correspond to a displacement of 0.01 millimeter.
  • the probe is mounted in coordinate positioning apparatus (the "machine" ⁇ such that the coordinate axes of the probe are parallel to the corresponding axes of the machine.
  • the stylus is provided at the free end thereof with a spherical element or ball whereby to engage the workpiece.
  • the probe is calibrated by setting the component outputs thereof to zero, and thereafter operating the machine to move the ball into engagement with respective datum surfaces provided at fixed positions in the machine, the direction of such engagement being substantially normal to the datum surfaces concerned.
  • Each such engagement produces a set of said component values which are fed into a computer for computation of a said resultant output and generation of a said step signal.
  • the step signal occurs at a given pre-travel following the instant of engagement. Since the trigger radius is the same for all directions of engagement, i.e. for any orientation of the datum surfaces, the pre-travels are similarly uniform.
  • the readings of the measuring devices of the apparatus are recorded as datum values and are fed to the computer.
  • the computer is programmed to compute the position of the centre of the ball, making allowance for the radius of the ball and of the trigger radius. It will be understood that the centre of the trigger radius and the centre of the ball coincide. The position of that common centre may be taken to define the rest position of the stylus. Measurement of the workpiece then proceeds by moving the stylus ball into engagement with the respective surfaces of the workpiece, recording the respective outputs of the machine scales and computing the actual positions of the surfaces by adding or subtracting, as the case may require, the ball and the trigger radii.
  • Fig.1 is an elevation of a coordinate measuring machine.
  • Fig.2 is an elevation of a probe used in the machine.
  • Fig.3 is a section on the line III-III in Fig.1
  • Fig.4 is a circuit diagram.
  • Fig.5 is an enlarged section on the line V-V In Fig.2.
  • the probe comprises a sensor 13 mounted in a coordinate measuring machine M comprising a combination of carriages 10,11,12 adapted to support the sensor 13, for movement relative to a workpiece 14 in the X,Y,Z directions of the rectangular coordinate system.
  • the movement of the sensor is measured by a combination of opto-electronic scales, e.g. 15, and digital counters 16 constituting the measuring system of the machine or the "machine scales".
  • the probe P is adapted to produce a step signal 17 when the machine is operated to move the sensor into engagement with a selected surface of the workpiece.
  • the signal 17 is connected to the counters 16 and the latter are adapted for the content thereof, at the instant of the signal 17, to be output as signals 18.
  • the latter signals define the coordinate position of the sensor 13 in terms of the outputs of the measuring system of the machine.
  • the sensor 13 comprises a stylus 20 having at one end a spherical sensing element or ball 21 whereby to engage the workpiece 14 as shown.
  • the other end of the stylus is secured to one end 23, the free end, of a coiled spring 22.
  • the other end, 24, of the spring is secured to a base 25 itself secured to the machine.
  • the base 25 has an axis 22A extending in the Z-direction.
  • the sensing element 21 is said to be at its rest position, and to be free, when no force acts thereon and it is said to be displaced when the machine is operated to bring the element 21 into engagement with the workpiece 14 and the force of such engagement moves the stylus away from the rest position.
  • the displacement takes place in opposition to the reaction force of the spring 22 which returns the element 21 to the rest position when the machine is. operated to withdraw the probe from the workpiece and the displacing force ceases.
  • Displacement of the element 21 in an X-Y plane causes the spring to bend approximately about a point 22B at the mid-length thereof.
  • Displacement of the element 21 in the Z-direction causes compression or extension of the spring 22.
  • the probe P itself has a short-range measuring system comprising four transducers 26 (Figs.2, 3) arranged symmetrically about the axis 22A and at the outside of the spring 22.
  • the arrangement is such that two diametrally opposite ones of the transducers lie in the X-Y plane while the other two transducers lie in the Y-Z plane. In this way the position of the transducers defines a pair of coordinate axes X,Y (Fig.3).
  • Each transducer 26 comprises an armature 27 (Fig.2) secured to the base 25 and a core 28 secured to the free end 23 of the spring through structure 29.
  • Each armature 27 comprises coils centred on an axis 26A parallel to the axis 22A and the associated core is correspondingly free to move in the Z-direction.
  • the transducers 26 are arranged so that, when the stylus 20 is at rest, the cores are situated at an X-Y plane approximately through the point 22B. Therefore, if the element 21 is displaced transversely to the Z-direction, the resulting arcuate movement of the cores about the point 22B takes place predominately In the Z-direction and an acceptably small radial clearance between each core and the associated coils is sufficient to accommodate the inevitable small X-Y component of the movement.
  • the transducers are connected to a discriminating circuit 30 for discriminating between X,Y and Z displacements of the element 21 and to produce corresponding analogue voltage signals X1, Y1 and Z1 which define the coordinate position of any displacement of the centre 21A of the element 21 from the rest position (Figs.4, 5).
  • the circuit 30 is known from our British Patent No. 1,573,447.
  • the signals X1,Y1,Z1 are taken through respective rectifiers 30A and calibrating potentiometers 30B to a zeroing or stabilising circuit 31 provided for stabilising the signals X1, Y1 Z1 against drift e.g. slow voltage changes due to temperature changes.
  • the stabilised signals are denoted X2,Y2,Z2.
  • a combining circuit 40 is provided for combining the signals X2,Y2,Z2 into a single signal 41 which, as will be seen, is a function of any displacement of the element 21 regardless of the direction of such displacement.
  • the step signal 17 is generated by a comparator 32 which changes the signal 17 from low to high when the signal 41 exceeds a given magnitude.
  • the circuit 31 comprises in respect of the output X1 and amplifier 35 producing said output X2, and the latter output is connected to a transconductance amplifier 36 adapted to produce a signal 37 showing excursions of the signal X2 from zero in a direction opposite to that of corresponding excursions of the signal X1.
  • the signal 37 is connected to the amplifier 35 whereby the signal X2 is biased to zero.
  • the signal 37 is also connected to earth through a capacitor 38 to produce a time constant by which the action of the amplifier 36 is delayed so that for rapid changes of the signal X1, such as would occur when the element 21 is engaged with the workpiece 14 during a measuring operation, the signal X2 is not affected and remains proportional to the signal X1.
  • the signal 17 can be generated as required.
  • the time constant is such that the signal X2 remains zero. In this way, when the element 21 is at rest between measuring operations, the signal X2 always has the zero value required as a preliminary to a measuring operation.
  • the signal 17 is connected to the amplifier 36 by a line 39 and such that when the signal 17 is high the amplifier 36 is inhibited. Thereby, if it should occur that the element 21 is held in engagement with the workpiece 14 for any length of time (and provided the displacement of the element 21 was sufficient to trigger the comparator 32), the signal X2 will not be affected and the signal 17 will remain high to signify that the is system still in the triggered condition. Circuit elements corresponding to the amplifiers 35,36, the capacitor 38 and the line 39 are also provided in respect of each of the signals Y1,Z1 to ensure that the signals Y2 , Z2 are biased to zero in circumstances like those described in respect of the signal X2.
  • this circuit combines the signal X2,Y2,Z2 into the single signal 41 Intended to be a function of displacement of the element 21 regardless of the direction of such displacement, i.e. regardless of whether or not the direction of displacement is aligned with the X,Y,Z directions.
  • Fig.5 shows the element 21 in engagement with a surface 14A of the workpiece 14 at a point 14B , the surface 14A lying at an angle to the X-Y axes of the sensor 13 and of the machine M, and the sensor having been moved toward the surface 14A in the direction of a line V normal to that surface .
  • the axis 22A coincided with the centre 21A.
  • the signals X2,Y2,Z2 are fed to respective squaring circuits 42 whose outputs 43 are connected to a summing circuit 44 whose output Is the signal 41.
  • the signal 41 is therefore proportional to the sum of the suares of the signals X2,Y2,Z2 in accordance with the formula (2) above.
  • the comparator 32 is connected to a bias feed 32A to produce the signal 17 when the value of the signal 41 reaches a given bias value or "trigger value" which, is this example is 1 volt, and the circuit 40 is calibrated for this value to correspond to a displacement equal to 0.01 millimeter. It will be clear that since the trigger value is 1 volt, i.e. unity, the square of r can be disregarded. A square root-forming circuit 44A may be introduced if a trigger value other than unity is to be used.
  • the sensor 13 has to travel 0.01 millimeter beyond the point of engagement between stylus and workpiece before the trigger signal occurs.
  • the distance of 0.01 millimeter is therefore the pre-travel of the probe and it will be clear that this pre-travel is not affected by the direction of the relative displacement between the stylus 20 and the base 25 of the probe.
  • the circuits 30,31,40 and the comparator 32 which constitute an analogue computer, are regarded as a part of the probe P because the signal 17 is the essential probe output as far as the trigger mode of operation is concerned.
  • the circuits 30,31,40 and the comparator 32 need not be in the same housing as the sensor 13 and may be embodied in an interface unit 50 (Fig.1) connected to the transducers 26 by a cable 51.
  • the counters 16 may form part of a digital computer 52 adapted to drive the carriages 10,11,12 and to store the signals 18 and to receive a trigger signal such as 17 all in a manner known per se in the context of known trigger probes
  • the outputs of the rectifiers 30A are connected by lines 30C directly to the computer 52 for use of the probe in a manner known per se for proportional probes.
  • the machine M, the probe 13 including the unit 50, and the computer 52 constitute a system for measuring workpieces.
  • the machine M includes a datum unit 53 (see also Fig.2, 3) for calibrating the system.
  • the unit 53 has a cube-shaped head 54 defining datum surfaces 55.
  • To calibrate the system the outputs X2,Y2,Z2 are allowed to attain zero and the sensor 13 is driven for the element 21 to engage the respective surfaces 55 to produce respective said signals 17.
  • the values of the corresponding signals 18 are then the datum values of the system.
  • Subsequent engagement of the element 21 with surfaces of the workpiece produces data relating those surfaces to the datum value as a basis for computation of the dimensions of the workpiece itself.
  • the radius of the element 21 and the pre-travel value r of the trigger sphere are taken into account again as known in connection with known trigger probes where, however, there existed the problem of having to cope with varying pre-travel values.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Length Measuring Devices With Unspecified Measuring Means (AREA)
  • Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)

Abstract

Une sonde de mesure des dimensions de pièces à usiner possède un élément capteur sphérique supporté sur une base et pouvant accomplir un mouvement dans les trois dimensions par rapport à la base, en réaction à l'engagement entre l'élément détecteur et une pièce à usiner. La sonde comprend des transducteurs (26) reliés à un circuit (30) permettant de déterminer le déplacement de l'élément capteur en fonction des valeurs des composantes du déplacement exprimées en coordonnées (X1, Y1, Z1). Afin de permettre d'utiliser la sonde comme sonde de déclenchement, un circuit (40) recombine les valeurs des composantes pour déterminer le déplacement original exprimé en une valeur résultante (41) et un comparateur (32) génère un signal de pas (17) lorsque la valeur résultante (41) dépasse une valeur-seuil donnée (r). Etant donné que la valeur-seuil est constante, le signal de pas (17) est produit en réaction au même déplacement de sa direction.
EP19850901523 1984-04-09 1985-04-09 Sonde de mesure de pieces a usiner Withdrawn EP0179083A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB848409091A GB8409091D0 (en) 1984-04-09 1984-04-09 Probe for measuring workpieces
GB8409091 1984-04-09

Publications (1)

Publication Number Publication Date
EP0179083A1 true EP0179083A1 (fr) 1986-04-30

Family

ID=10559386

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19850901523 Withdrawn EP0179083A1 (fr) 1984-04-09 1985-04-09 Sonde de mesure de pieces a usiner

Country Status (4)

Country Link
EP (1) EP0179083A1 (fr)
JP (1) JPS61501793A (fr)
GB (1) GB8409091D0 (fr)
WO (1) WO1985004706A1 (fr)

Families Citing this family (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0242710B1 (fr) * 1986-04-17 1990-07-25 Renishaw plc Sonde pour palpeur de contact
GB8610087D0 (en) * 1986-04-24 1986-05-29 Renishaw Plc Probe
GB8610088D0 (en) * 1986-04-24 1986-05-29 Renishaw Plc Probe
US4916339A (en) * 1986-09-03 1990-04-10 Renishaw Plc Signal processing for contact-sensing probe
GB8713715D0 (en) * 1987-06-11 1987-07-15 Renishaw Plc Workpiece inspection method
EP0521703B1 (fr) * 1991-07-03 1995-11-02 Renishaw Metrology Limited Circuit de traitement de signal pour sonde à déclenchement
GB9224335D0 (en) * 1992-11-20 1993-01-13 Renishaw Metrology Ltd A method of measuring workpieces using a surface contacting measuring probe
GB0509394D0 (en) 2005-05-10 2005-06-15 Renishaw Plc Dimensional measurement probe
CN113175861A (zh) * 2021-04-01 2021-07-27 东风柳州汽车有限公司 检具及钣金件加工系统

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2841548A1 (de) * 1978-09-23 1980-04-03 Leitz Ernst Gmbh Verfahren und einrichtung zur messwerterfassung an prueflingen
DD141197A1 (de) * 1978-12-27 1980-04-16 Horst Donat Koordinatentastkopf zum antasten mehrdimensionaler werkstuecke
GB2045437B (en) * 1979-03-30 1984-02-08 Renishaw Electrical Ltd Coordinate measuring machine
GB2049198B (en) * 1979-05-01 1983-03-30 Renishaw Electrical Ltd Probe for use in measuring apparatus
US4443946A (en) * 1980-07-01 1984-04-24 Renishaw Electrical Limited Probe for measuring workpieces
DE3210711C2 (de) * 1982-03-24 1986-11-13 Dr.-Ing. Höfler Meßgerätebau GmbH, 7505 Ettlingen Mehrkoordinatentaster mit einstellbarer Meßkraft zum Abtasten von mehrdimensionalen, stillstehenden Gegenständen

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8504706A1 *

Also Published As

Publication number Publication date
JPS61501793A (ja) 1986-08-21
WO1985004706A1 (fr) 1985-10-24
GB8409091D0 (en) 1984-05-16

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Inventor name: ROGERS, MICHAEL, JOHN