WO2015166035A1 - Apparatus and method for checking the position and/or dimensions of a workpiece - Google Patents

Apparatus and method for checking the position and/or dimensions of a workpiece Download PDF

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Publication number
WO2015166035A1
WO2015166035A1 PCT/EP2015/059494 EP2015059494W WO2015166035A1 WO 2015166035 A1 WO2015166035 A1 WO 2015166035A1 EP 2015059494 W EP2015059494 W EP 2015059494W WO 2015166035 A1 WO2015166035 A1 WO 2015166035A1
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WIPO (PCT)
Prior art keywords
feeler
checking
point
workpiece
sensor
Prior art date
Application number
PCT/EP2015/059494
Other languages
French (fr)
Inventor
Stefano Pareschi
Samuele Martelli
Riccardo Cipriani
Original Assignee
Marposs Societa' Per Azioni
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Publication date
Application filed by Marposs Societa' Per Azioni filed Critical Marposs Societa' Per Azioni
Publication of WO2015166035A1 publication Critical patent/WO2015166035A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B5/00—Measuring arrangements characterised by the use of mechanical techniques
    • G01B5/20—Measuring arrangements characterised by the use of mechanical techniques for measuring contours or curvatures
    • G01B5/202—Measuring arrangements characterised by the use of mechanical techniques for measuring contours or curvatures of gears
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B5/00—Measuring arrangements characterised by the use of mechanical techniques
    • G01B5/14—Measuring arrangements characterised by the use of mechanical techniques for measuring distance or clearance between spaced objects or spaced apertures
    • G01B5/16—Measuring arrangements characterised by the use of mechanical techniques for measuring distance or clearance between spaced objects or spaced apertures between a succession of regularly spaced objects or regularly spaced apertures
    • G01B5/166—Measuring arrangements characterised by the use of mechanical techniques for measuring distance or clearance between spaced objects or spaced apertures between a succession of regularly spaced objects or regularly spaced apertures of gear teeth

Definitions

  • the present invention relates to an apparatus and a method for checking the position and/or dimensions of mechanical parts or workpieces, by using at least one touch trigger probe and a checking system for checking or measuring the position of the probe in a reference system.
  • the invention can be advantageously applied to carry out dimensional checking of gears and toothed wheels, and more specifically for checking helical gears.
  • a touch trigger probe is displaced so that its feeler - typically a spherical feeler - moves towards the tooth surface along a checking direction to touch the surface at that point the position of which must be detected.
  • the probe After the contact has taken place, and the feeler has displaced of a known amount, called "pre-stroke” , the probe transmits a signal to a control system that stops the movement between the touch trigger probe and the tooth, and determines the position of the former in the reference system, more specifically determines the position of a probe axis.
  • the pre-stroke of the probe is acquired during a preliminary calibration stage that is carried out using master parts (rings, spheres,%) having known dimensions.
  • the position of the point to be detected in the reference system is obtained, starting from the probe position and subtracting or adding the known pre-stroke, depending on the probe movement in the reference system, in one sense or the other.
  • the position of two points PI and P2 must be detected, by bringing the probe to touch the gear in opposite senses along the checking direction Dc.
  • An object of the invention is to provide a checking system and a checking method that overcome the problems of the known solutions, more specifically allow to get reliable results without the need to render the movements between probe and workpiece too complex.
  • An apparatus comprises a reference system with driving and detecting devices and a touch trigger probe with a support, connected to the driving and detecting devices, that defines a reference axis, an armset movable with respect to the support, a feeler fixed to the armset and adapted to contact one point of a surface of the workpiece to be checked by a mutual approaching movement along a checking direction defined by the driving and detecting devices, and a sensor that provides a touch signal following the contact between the feeler and the workpiece to be checked.
  • a process and control unit that is connected to the driving and detecting devices and to the sensor of the touch trigger probe, is configured, in order to compensate for the slipping, to process the touch signal provided by the sensor together with information about an angular arrangement of the checking direction with respect to a direction perpendicular to the surface of the workpiece to be checked at one point the position of which has to be checked.
  • the position of the center of the feeler at the instant of contact, that is indicative of the position of the point to be checked is calculated on the basis a position value acquired by the driving and detecting devices when the touch signal is provided by the sensor, by adding or subtracting a compensation amount that takes into account the pre-stroke of the probe and the angular arrangement of the checking direction.
  • Specific methods include additional steps for checking the thickness of the teeth or carrying out span measurements of helical gears.
  • - figure 1 is a partial, schematic view of a gear to be checked
  • - figure 2 is a perspective view of a gear to be checked, with a schematically represented probe that is part of an apparatus according to the invention
  • FIG. 3 is a front view of the gear, with the probe and a schematically represented apparatus according to the invention
  • FIG. 4 is a schematical representation, showing a feeler of the probe and an inclined surface to be checked, of a checking phase of a method according to the invention
  • FIG. 5 is a schematical representation of checking phases of a method according to a preferred embodiment of the invention for checking linear dimensions, e.g. the thickness, of a workpiece;
  • FIG. 6 is a schematical representation of checking phases of a method according to an alternative embodiment of the invention for checking linear dimensions, e.g. the thickness, of a workpiece.
  • a checking apparatus includes a known probe, or touch trigger probe, 1, with a support or housing 3 defining a reference axis A, an armset 6 movable with respect to the support 3, a feeler 7, fixed to the armset 6, and a sensor 5, coupled to a processing and control unit 20 and configured to send signals to said processing and control unit 20.
  • the feeler 7 has the shape of a sphere, with a center C that, in a rest condition of the probe 1, that is in a rest condition of the armset 6 with respect to the support 3, is substantially aligned with the reference axis A.
  • the apparatus that has features known per se and shown in figure 3 in a very schematic way, further includes a reference system 9 (axes X, Y and Z) with driving and detecting devices 11 carrying the support 3 of the probe 1 and coupled to the processing and control unit 20.
  • a reference system 9 axes X, Y and Z
  • driving and detecting devices 11 carrying the support 3 of the probe 1 and coupled to the processing and control unit 20.
  • the checking direction Dc is inclined with respect to the surface S and, in general, to the faces of the teeth T of the helical gear G .
  • Figure 4 shows an outer circle, schematically representing an enlarged view of the feeler 7 on plane X-Y, with center C , and a concentric inner circle 7p, the radius of which represents a distance value (between center C and axis A) , along a direction radial with respect to the reference axis A, between an inoperative position of the feeler 7 and a position corresponding to a predetermined arrangement of the armset 6 with respect to the support 3.
  • such distance value, or pre-stroke Rp of the probe 1 is the value of a known displacement amount of the feeler 7 between a position, corresponding to the rest condition of the armset 6, as it is before touching the workpiece, and the above-mentioned position corresponding to the above- mentioned predetermined arrangement of the movable armset 6 with respect to the support 3, arrangement at which the sensor 5 transmits a relevant signal, i.e. a touch signal, to the processing and control unit 20.
  • the closing movements between the feeler 7 and the surface S of the tooth T take place along the checking direction Dc (that is parallel to the X axis in the reference system 9) until a contact between the feeler 7 and the surface S takes place at a substantially punctiform area, more specifically at point P .
  • the checking direction Dc is angularly arranged with respect to a perpendicular direction Do that is perpendicular to the surface S of a non-negligible angle ⁇ (angular arrangement value, for instance of about 20°/30°) in the plane X-Y, that is perpendicular to reference axis A.
  • the feeler 7, that moves along the checking direction Dc after having touched the surface S at point P and during a limited additional displacement of the probe 1, slips on the surface S (dashed arc 7' ) up to a point P ' at which the sensor 5 of the probe 1, after a displacement of an amount Ts larger that the pre-stroke Rp, sends a touch signal to the processing and control unit 20.
  • the movement along the checking direction Dc stops and the driving and checking devices 11 detect the position of the probe 1, more specifically a position value X0 of the reference axis A defined by the support 3 is acquired when the touch signal is provided by the sensor 5.
  • the position XC of the center C of the feeler 7 at the instant of the contact at point P is obtained starting from the determined position X0, and taking into account not only the known pre-stroke Rp, but also the angular arrangement value ⁇ , according to the following formula
  • a first face with surface SI and a second face with surface S2 of a tooth T are schematically shown, and circles representing the feeler 7 of the probe 1 are shown in two operative positions, having centers CI and C2, respectively, when touching surface SI at point Pi and surface S2 at point P2, respectively.
  • the thickness of tooth T that is the distance TH between surfaces SI and S2, is calculated as follows:
  • (a) coordinate XI is detected when the processing and control unit 20 receives a touch signal transmitted by the sensor 5 of the probe 1 as a consequence of a contact between the feeler 7, during a movement of the latter along a first checking direction Del towards positive X values, and the surface SI at point Pi.
  • Corresponding coordinate Yl in the reference system is known and does not vary in the movement along the first checking direction Del. In this way, a position value XI, Yl relative to the contact of the feeler 7 at the first point Pi of the first surface SI is acquired;
  • 3, that compensates for slipping of the feeler 7, and consequently of the contact point Pi, schematically shown in figure 5 by dashed arc 7' . Since YCl Yl, both the coordinates XC1, YCl of the position of the center CI of the feeler 7 in the X-Y plane at the contact with point Pi are known;
  • coordinate X2 is detected when the processing and control unit 20 receives a touch signal provided by the sensor 5 of the probe 1 as a consequence of a contact between the feeler 7, moving along the second checking direction Dc2 towards negative X values, and the surface S2 at point P2. In this way, a position value X2, Y2 relative to the contact of the feeler 7 at the second point P2 of the second surface S2 is acquired;
  • XC2 X2 - Rp/cos
  • the angular arrangement value ⁇ can be calculated before the start of checking phase on the basis of detections of the probe 1, for instance by moving such probe 1 to touch the surface (s) to be checked along two or more directions parallel to the X axis and spaced apart of a known amount .
  • the feeler 7, and consequently contact points Pi and P2 are assumed not to undergo any significant slipping.
  • Figure 6 shows a different method, according to an alternative embodiment of the invention, for checking the thickness TH of the tooth T.
  • Some steps of this different method are the same as the ones of the method described with reference to figure 5, more specifically the steps that take into account and compensate for the pre-stroke Rp and for the slipping of the feeler 7 on the surfaces of the tooth T.
  • Different steps of this different method involve displacements of the probe 1 along Y axis after the feeler 7 has touched the first surface SI to define an alternative second checking direction and a contact point on the second surface S2.
  • the method of figure 6 includes the following steps:
  • step (a') the same as step (a) described above with reference to figure 5, that is: coordinate XI is detected when the processing and control unit 20 receives a touch signal transmitted by the sensor 5 of the probe 1 as a consequence of a contact between the feeler 7, during a movement of the latter along a first checking direction
  • 3, that compensates for slipping of the feeler 7, and consequently of the contact point Pi, schematically shown in figure 6 by dashed arc 7' . Since YCl Yl, both the coordinates XC1, YCl of the position of the center CI of the feeler 7 in the X-Y plane at the contact with point Pi are known;
  • step (d') it is substantially the same, except for the different coordinate Y2a, as step (d) described above with reference to figure 5 that is: coordinate X2a is detected when the processing and control unit 20 receives a touch signal transmitted by the sensor 5 of the probe 1 as a consequence of a contact between the feeler 7, moving along the alternative second checking direction Dc2a towards negative X values, and the surface S2 at point P2a. In this way, a position value X2a, Y2a relative to the contact of the feeler 7 at the second point P2a of the second surface S2 is acquired;
  • CC sqr [ (XC1 - XC2a) 2 + (YCl - YC2a) 2 ] (g') the component CCo of the centers distance CC along perpendicular direction Do that is perpendicular to surfaces SI and S2 is calculated as follows:
  • CCo CC cos ( ⁇ - ⁇ )
  • a is the inclination angle between the X axis (and as a consequence the checking directions Del, Dc2a) and the straight line on which both CI and C2a lie, and can be calculated as follows:
  • the above described methods for checking the thickness TH of a tooth T can be employed for checking different dimensions of the workpiece, for instance the span or Wildhaber measurement W3 of a helical gear or toothed wheel as shown in figure 1, where the surfaces SI and S2 are surfaces of mutually opposed faces of two different teeth.
  • Apparatuses and methods according to the present invention can include different features with respect to what is shows in the drawings and described above.
  • the feeler can have a shape that is different with respect to a spherical one.
  • an apparatus and a method according to the invention can be used for checking position and/or dimensions of parts different with respect to gears and toothed wheels, parts including in any case surfaces that are inclined with respect to checking directions on which the feeler of the touch trigger probe is moving.

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  • General Physics & Mathematics (AREA)
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Abstract

An apparatus and a method for checking the position and/or dimensions of a workpiece, more specifically dimensions of teeth (T) of gears, make use of a touch trigger probe (1) having a determined pre-stroke (Rp) and driving and detecting devices (11) to check a position of the probe in a reference system (9). A feeler (7) of the probe approaches and contacts a surface (S) of the tooth to be checked along a checking direction (Dc) that is inclined with respect to a direction (Do) perpendicular to the same surface. The position of a point (P) on the surface of the tooth is detected on the basis of the position (XC) of the center (C) of the feeler when the contact takes place that, in its turn, is based on the indication provided by the driving and detecting devices and a processing that takes into account the pre-stroke and the angular arrangement (P) of the checking direction. Specific methods for checking the tooth thickness or other dimensions of the gear include additional steps.

Description

DESCRIPTION
« APPARATUS AND METHOD FOR CHECKING THE POSITION AND/OR DIMENSIONS OF A WORKPIECE »
Technical Field
The present invention relates to an apparatus and a method for checking the position and/or dimensions of mechanical parts or workpieces, by using at least one touch trigger probe and a checking system for checking or measuring the position of the probe in a reference system.
The invention can be advantageously applied to carry out dimensional checking of gears and toothed wheels, and more specifically for checking helical gears.
Prior Art
Arrangements are known wherein, in order to check a workpiece, more specifically to detect the position of a point on a tooth surface of a gear (or of a toothed wheel) , in a reference system, a touch trigger probe is displaced so that its feeler - typically a spherical feeler - moves towards the tooth surface along a checking direction to touch the surface at that point the position of which must be detected.
After the contact has taken place, and the feeler has displaced of a known amount, called "pre-stroke" , the probe transmits a signal to a control system that stops the movement between the touch trigger probe and the tooth, and determines the position of the former in the reference system, more specifically determines the position of a probe axis. The pre-stroke of the probe is acquired during a preliminary calibration stage that is carried out using master parts (rings, spheres,...) having known dimensions.
The position of the point to be detected in the reference system is obtained, starting from the probe position and subtracting or adding the known pre-stroke, depending on the probe movement in the reference system, in one sense or the other.
In order to measure or check the tooth thickness, or other featuring dimensions of the part, for instance the span between faces delimiting a group of three teeth at a predetermined radial distance from the center of the gear (span or Wildhaber measurement W3 as shown in the schematic view of figure 1), the position of two points PI and P2 must be detected, by bringing the probe to touch the gear in opposite senses along the checking direction Dc.
When the checking direction Dc along which the probe approaches the surface to be checked is not perpendicular or substantially perpendicular to the latter, the checking is not fully reliable.
This is a particular issue when checking helical gears
(figures 2 and 3) whose teeth T have faces with surfaces S sloping and not perpendicular with respect to the lateral sides F , also in view of the fact that is generally rather complex to define and put into practice movements between probe and workpiece that are always perpendicular to the surface to be checked.
Disclosure of the Invention
An object of the invention is to provide a checking system and a checking method that overcome the problems of the known solutions, more specifically allow to get reliable results without the need to render the movements between probe and workpiece too complex.
This and other objects are achieved by an apparatus and a method according to the appended claims.
An apparatus according to the invention comprises a reference system with driving and detecting devices and a touch trigger probe with a support, connected to the driving and detecting devices, that defines a reference axis, an armset movable with respect to the support, a feeler fixed to the armset and adapted to contact one point of a surface of the workpiece to be checked by a mutual approaching movement along a checking direction defined by the driving and detecting devices, and a sensor that provides a touch signal following the contact between the feeler and the workpiece to be checked. While the checking direction is inclined with respect to the surface that is touched and the feeler is subject to slipping, a process and control unit, that is connected to the driving and detecting devices and to the sensor of the touch trigger probe, is configured, in order to compensate for the slipping, to process the touch signal provided by the sensor together with information about an angular arrangement of the checking direction with respect to a direction perpendicular to the surface of the workpiece to be checked at one point the position of which has to be checked.
According to a method that makes use of an apparatus including a touch trigger probe with a feeler having a spherical shape, the position of the center of the feeler at the instant of contact, that is indicative of the position of the point to be checked, is calculated on the basis a position value acquired by the driving and detecting devices when the touch signal is provided by the sensor, by adding or subtracting a compensation amount that takes into account the pre-stroke of the probe and the angular arrangement of the checking direction.
Specific methods include additional steps for checking the thickness of the teeth or carrying out span measurements of helical gears.
Brief Description of the Drawings
An apparatus and a method according to the present invention are hereinafter described with reference to the attached sheets of drawings given by way of non-limiting examples, wherein:
- figure 1 is a partial, schematic view of a gear to be checked; - figure 2 is a perspective view of a gear to be checked, with a schematically represented probe that is part of an apparatus according to the invention;
- figure 3 is a front view of the gear, with the probe and a schematically represented apparatus according to the invention;
- figure 4 is a schematical representation, showing a feeler of the probe and an inclined surface to be checked, of a checking phase of a method according to the invention;
- figure 5 is a schematical representation of checking phases of a method according to a preferred embodiment of the invention for checking linear dimensions, e.g. the thickness, of a workpiece; and
- figure 6 is a schematical representation of checking phases of a method according to an alternative embodiment of the invention for checking linear dimensions, e.g. the thickness, of a workpiece.
Best Mode for Carrying Out the Invention
Making reference to figures 2 and 3, a checking apparatus according to the present invention includes a known probe, or touch trigger probe, 1, with a support or housing 3 defining a reference axis A, an armset 6 movable with respect to the support 3, a feeler 7, fixed to the armset 6, and a sensor 5, coupled to a processing and control unit 20 and configured to send signals to said processing and control unit 20. In the preferred embodiment of the figures, the feeler 7 has the shape of a sphere, with a center C that, in a rest condition of the probe 1, that is in a rest condition of the armset 6 with respect to the support 3, is substantially aligned with the reference axis A. The apparatus, that has features known per se and shown in figure 3 in a very schematic way, further includes a reference system 9 (axes X, Y and Z) with driving and detecting devices 11 carrying the support 3 of the probe 1 and coupled to the processing and control unit 20. When the position of a point P in a surface S of a tooth T of a workpiece, more specifically a helical gear or toothed wheel, G is to be detected by means of the checking apparatus, a mutual approaching movement between the feeler 7 and the surface S is caused to take place. More specifically, the probe 1 is caused to displace with respect to the gear G so that the feeler 7 moves along a checking direction Dc that is substantially parallel to the lateral side F of the gear G (figures 2 and 3) . The checking direction Dc is inclined with respect to the surface S and, in general, to the faces of the teeth T of the helical gear G . Figure 4 shows an outer circle, schematically representing an enlarged view of the feeler 7 on plane X-Y, with center C , and a concentric inner circle 7p, the radius of which represents a distance value (between center C and axis A) , along a direction radial with respect to the reference axis A, between an inoperative position of the feeler 7 and a position corresponding to a predetermined arrangement of the armset 6 with respect to the support 3. More specifically, such distance value, or pre-stroke Rp of the probe 1, is the value of a known displacement amount of the feeler 7 between a position, corresponding to the rest condition of the armset 6, as it is before touching the workpiece, and the above-mentioned position corresponding to the above- mentioned predetermined arrangement of the movable armset 6 with respect to the support 3, arrangement at which the sensor 5 transmits a relevant signal, i.e. a touch signal, to the processing and control unit 20. In the situation shown in figure 4, the closing movements between the feeler 7 and the surface S of the tooth T take place along the checking direction Dc (that is parallel to the X axis in the reference system 9) until a contact between the feeler 7 and the surface S takes place at a substantially punctiform area, more specifically at point P . The checking direction Dc is angularly arranged with respect to a perpendicular direction Do that is perpendicular to the surface S of a non-negligible angle β (angular arrangement value, for instance of about 20°/30°) in the plane X-Y, that is perpendicular to reference axis A.
As a consequence of this angular arrangement, the feeler 7, that moves along the checking direction Dc , after having touched the surface S at point P and during a limited additional displacement of the probe 1, slips on the surface S (dashed arc 7' ) up to a point P ' at which the sensor 5 of the probe 1, after a displacement of an amount Ts larger that the pre-stroke Rp, sends a touch signal to the processing and control unit 20. The movement along the checking direction Dc stops and the driving and checking devices 11 detect the position of the probe 1, more specifically a position value X0 of the reference axis A defined by the support 3 is acquired when the touch signal is provided by the sensor 5.
In a method according to the present invention, the position XC of the center C of the feeler 7 at the instant of the contact at point P is obtained starting from the determined position X0, and taking into account not only the known pre-stroke Rp, but also the angular arrangement value β , according to the following formula
XC = X0 ± Rp/cosp
where Rp/cos|3 is the value Ts that must be subtracted or added, depending on the probe movement in the reference system, to the position value X0 of the reference axis A as detected, to compensate for both the pre-stroke Rp and the slipping of the feeler 7 on the surface S of the tooth T with respect to an ideal fully rigid system, without pre- stroke (i.e. Rp = 0) and without slipping, wherein the contact at point P would be revealed by the position of the center C of the feeler 7, laying on the reference axis A, as immediately signalled by the sensor 5, without any hysteresis .
In figure 5, a first face with surface SI and a second face with surface S2 of a tooth T are schematically shown, and circles representing the feeler 7 of the probe 1 are shown in two operative positions, having centers CI and C2, respectively, when touching surface SI at point Pi and surface S2 at point P2, respectively.
The thickness of tooth T, that is the distance TH between surfaces SI and S2, is calculated as follows:
(a) coordinate XI is detected when the processing and control unit 20 receives a touch signal transmitted by the sensor 5 of the probe 1 as a consequence of a contact between the feeler 7, during a movement of the latter along a first checking direction Del towards positive X values, and the surface SI at point Pi. Corresponding coordinate Yl in the reference system is known and does not vary in the movement along the first checking direction Del. In this way, a position value XI, Yl relative to the contact of the feeler 7 at the first point Pi of the first surface SI is acquired;
(b) coordinate XC1 is calculated by means of the previously cited formula, that is XC1 = XI - Rp/cos|3, that compensates for slipping of the feeler 7, and consequently of the contact point Pi, schematically shown in figure 5 by dashed arc 7' . Since YCl = Yl, both the coordinates XC1, YCl of the position of the center CI of the feeler 7 in the X-Y plane at the contact with point Pi are known;
(c) the probe 1 is moved along the Y axis to a coordinate YC2, corresponding to a second checking direction Dc2 parallel to the first checking direction Del, so that feeler 7, moving along the second checking direction Dc2 towards negative X values can touch surface S2 at a point P2 that lies on the perpendicular direction Do that is perpendicular to surfaces SI and S2 and on which Pi lies, too. More specifically, the amount of the displacement along axis is d = (2r + THn)sen|3, where 2r is the nominal diameter of feeler 7, and THn is the nominal thickness of tooth T, i.e. the nominal distance between surfaces SI and S2, so coordinate YC2 of center C2 is calculated as YC2 = YCl -d; (d) coordinate X2 is detected when the processing and control unit 20 receives a touch signal provided by the sensor 5 of the probe 1 as a consequence of a contact between the feeler 7, moving along the second checking direction Dc2 towards negative X values, and the surface S2 at point P2. In this way, a position value X2, Y2 relative to the contact of the feeler 7 at the second point P2 of the second surface S2 is acquired;
(e) coordinate XC2 is calculated by means of the previously cited formula, that is XC2 = X2 - Rp/cos|3, that compensates for slipping of the feeler 7, and consequently of contact point P2, schematically shown in figure 5 by dashed arc 7' . Both coordinates XC2, YC2 of the position of the center C2 of the feeler 7 in the X-Y plane at the contact with point P2 are so known;
(f) the thickness TH of the tooth T, that is the distance between the first and second surfaces SI and S2, is calculated as follows:
TH = sqr [ (XC1 - XC2 ) 2 + (YCl - YC2 ) 2 ] - 2r The angular arrangement value β can be calculated before the start of checking phase on the basis of detections of the probe 1, for instance by moving such probe 1 to touch the surface (s) to be checked along two or more directions parallel to the X axis and spaced apart of a known amount .
When the angular arrangement value β is small (10° or less) the feeler 7, and consequently contact points Pi and P2, are assumed not to undergo any significant slipping. As a consequence, the method for checking the thickness of the tooth T may be simplified making the hypothesis that XC1 = XI - Rp and XC2 = X2 - Rp.
Figure 6 shows a different method, according to an alternative embodiment of the invention, for checking the thickness TH of the tooth T. Some steps of this different method are the same as the ones of the method described with reference to figure 5, more specifically the steps that take into account and compensate for the pre-stroke Rp and for the slipping of the feeler 7 on the surfaces of the tooth T. Different steps of this different method involve displacements of the probe 1 along Y axis after the feeler 7 has touched the first surface SI to define an alternative second checking direction and a contact point on the second surface S2.
More specifically, the method of figure 6 includes the following steps:
(a') the same as step (a) described above with reference to figure 5, that is: coordinate XI is detected when the processing and control unit 20 receives a touch signal transmitted by the sensor 5 of the probe 1 as a consequence of a contact between the feeler 7, during a movement of the latter along a first checking direction
Del towards positive X values, and the surface SI at point Pi. Corresponding coordinate Yl in the reference system is known and does not vary in the movement along the first checking direction Del. In this way, a position value XI, Yl relative to the contact of the feeler 7 at the first point Pi of the first surface SI is acquired;
(b ' ) the same as step (b) described above with reference to figure 5, that is: coordinate XC1 is calculated by means of formula XC1 = XI - Rp/cos|3, that compensates for slipping of the feeler 7, and consequently of the contact point Pi, schematically shown in figure 6 by dashed arc 7' . Since YCl = Yl, both the coordinates XC1, YCl of the position of the center CI of the feeler 7 in the X-Y plane at the contact with point Pi are known;
(c') the probe 1 is moved along the Y axis to a coordinate Y2a = YC2a that defines an alternative second checking direction Dc2a parallel to the first checking direction Del, so that feeler 7, moving along the alternative second checking direction Dc2a towards negative X values can touch surface S2 at a point P2a that is roughly opposed to point Pi of surface SI. Contrary to step (c) of the method of figure 5, no calculation is made to align points Pi and P2a along perpendicular direction Do;
(d') it is substantially the same, except for the different coordinate Y2a, as step (d) described above with reference to figure 5 that is: coordinate X2a is detected when the processing and control unit 20 receives a touch signal transmitted by the sensor 5 of the probe 1 as a consequence of a contact between the feeler 7, moving along the alternative second checking direction Dc2a towards negative X values, and the surface S2 at point P2a. In this way, a position value X2a, Y2a relative to the contact of the feeler 7 at the second point P2a of the second surface S2 is acquired;
(e') it is substantially the same, except for the different coordinate Y2a, as step (e) described above with reference to figure 5 that is: coordinate XC2a is calculated by means of formula XC2 = X2 - Rp/cos|3, that compensates for slipping of the feeler 7, and consequently of contact point P2a, schematically shown in figure 6 by dashed arc 7' . Both coordinates X2a, Y2a of the center C2a of the feeler 7 in the X-Y plane at the contact with point P2a are so known;
( f ) a centers distance CC between centers CI and C2a is calculated as follows:
CC = sqr [ (XC1 - XC2a) 2 + (YCl - YC2a)2] (g') the component CCo of the centers distance CC along perpendicular direction Do that is perpendicular to surfaces SI and S2 is calculated as follows:
CCo = CC cos (α - β)
where a is the inclination angle between the X axis (and as a consequence the checking directions Del, Dc2a) and the straight line on which both CI and C2a lie, and can be calculated as follows:
a = arc tan [ (YCl - YC2a) / (XC1 - XC2a) ] ; (η') the value of the thickness TH of the tooth T, that is the distance between surfaces SI and S2, is obtained, by subtracting the diameter of the feeler 7 from CCo, as follows:
TH = CCo - 2r.
The above described methods for checking the thickness TH of a tooth T can be employed for checking different dimensions of the workpiece, for instance the span or Wildhaber measurement W3 of a helical gear or toothed wheel as shown in figure 1, where the surfaces SI and S2 are surfaces of mutually opposed faces of two different teeth.
Apparatuses and methods according to the present invention can include different features with respect to what is shows in the drawings and described above. For instance, the feeler can have a shape that is different with respect to a spherical one. Moreover, an apparatus and a method according to the invention can be used for checking position and/or dimensions of parts different with respect to gears and toothed wheels, parts including in any case surfaces that are inclined with respect to checking directions on which the feeler of the touch trigger probe is moving.

Claims

1. Apparatus for checking the position and/or dimensions of a workpiece, comprising:
• a reference system (9) with driving and detecting devices (11);
• a touch trigger probe (1) with
0 a support (3) connected to the driving and detecting devices (11), that defines a reference axis (A),
0 an armset (6) movable with respect to the support (3),
0 a feeler (7) fixed to the armset (6), and adapted to contact one point (P) of a surface (S) of the workpiece to be checked by a mutual approaching movement along a checking direction (Dc) , and
0 a sensor (5) adapted to provide a touch signal indicative of the contact between the feeler (7) and said surface (S) of the workpiece to be checked; and
• a processing and control unit (20) connected to the driving and detecting devices (11) and to the sensor (5) of the touch trigger probe (1) and adapted to detect the position of said one point (P) of said surface (S) of the workpiece to be checked in the reference system (9) on the basis of the touch signal provided by the sensor (5) ,
the driving and detecting devices (11) defining said checking direction (Dc) , the latter being inclined with respect to said surface (S) of the workpiece at said one point (P) ,
characterized in that the processing and control unit (20) is configured to process information about an angular arrangement (β) of the checking direction (Dc) with respect to a perpendicular direction (Do) that is perpendicular to the surface (S) of the workpiece to be checked at said one point (P) , in order to compensate for slipping of the feeler (7) on the surface (S) and detect the position of said one point (P) of the surface (S) of the workpiece to be checked.
2. Apparatus according to claim 1, wherein the feeler (7) has the shape of a sphere having a center (C) that is substantially aligned to said reference axis (A) when the armset (6) is in a rest condition with respect to the support (3) and that is adapted to move along said checking direction (Dc) , the process and control unit (20) being adapted to detect the position of said one point (P) of the surface (S) by calculating a position (XC) of said center (C) at the instant of the contact with said one point (P) as follows
XC = X0 ± Κρ/οοεβ
wherein
X0 is a position value acquired by the driving and detecting devices (11) when the touch signal is provided by the sensor (5) , and
Rp is a pre-stroke (Rp) of the touch trigger probe (1), that is a distance value, along a direction radial with respect to said reference axis (A) , between two positions of the feeler (7) corresponding, respectively, to the rest condition of the armset (6) and to a predetermined arrangement of the armset (6) with respect to the support (3) at which the sensor (5) provides the touch signal.
3. Method for checking the position and/or dimensions of a workpiece by means of an apparatus comprising a reference system (9) with driving and detecting devices (11) defining a checking direction (Dc) , a touch trigger probe (1) with a support (3), connected to the driving and detecting devices (11), that defines a reference axis (A), said checking direction (Dc) being substantially perpendicular to the reference axis (A), an armset (6) movable with respect to the support (3), a feeler (7) fixed to the armset (6) substantially aligned to said reference axis (A) when the armset (6) is in a rest condition with respect to the support (3) , and a sensor (5) adapted to provide a touch signal indicative of a contact between the feeler (7) and a surface (S) of the workpiece to be checked, and a processing and control unit (20) connected to the driving and detecting devices (11) and to the sensor (5) of the touch trigger probe (1) and adapted to detect the position of said one point (P) of said surface (S) of the workpiece to be checked in the reference system (9) on the basis of the touch signal provided by the sensor (5) , the method including the following steps:
• defining a pre-stroke (Rp) of the touch trigger probe (1) as a distance value, along a direction radial with respect to said reference axis (A) , between positions of the feeler (7) corresponding to the rest condition of the armset (6) and a predetermined arrangement of the armset (6) with respect to the support (3) at which the sensor (5) provides the touch signal,
• defining an angular arrangement value (β) of said checking direction (Dc) with respect to a perpendicular direction (Do) that is perpendicular to the surface (S) of the workpiece to be checked,
• mutually moving the touch trigger probe (1) and the workpiece to be checked, so that the feeler (7) approaches said surface (S) of the workpiece along said checking direction (Dc) and contacts said surface (S) at said one point (P) ,
• providing, by the sensor (5) , the touch signal when, as a consequence of such contact, said predetermined arrangement of the armset (6) with respect to the support (3) is reached,
• acquiring a position value (X0) by means of the driving and detecting devices (11) when the touch signal is provided by the sensor (5) , and
• processing said position value (X0) together with the pre-stroke (Rp) and the angular arrangement value (β) in order to compensate for slipping of the feeler (7) on the surface (S) and detect the position of said one point (P) of said surface (S) of the workpiece to be checked .
4. Method according to claim 3, wherein said angular arrangement value (β) of the checking direction (Dc) is defined with respect to said perpendicular direction (Do) that is also perpendicular to said reference axis (A) .
5. Method according to claim 3 or claim 4, wherein the feeler (7) that is used has the shape of a sphere, and the position of a center (XC) of the sphere is detected at the instant of the contact with said one point (P) of the surface of the workpiece by processing said position value (XO), pre-stroke (Rp) and angular arrangement value (β) according to the formula
XC = XO ± Κρ/οοεβ.
6. Method according to claim 5, for checking the distance (TH) between a first surface (SI) and a second surface (S2) of one or more teeth (T) of a gear or toothed wheel, the method including the following steps:
(a) during a movement of the feeler (7) along a first checking direction (Del), acquiring a position value (XI, Yl) relative to the contact of the feeler (7) at a first point (PI) of the first surface (SI) when the touch signal is provided by the sensor (5) ;
(b) calculating a first position of the center (XC1,YC1) of the feeler (7) by means of the formula XC1 = XI - Κρ/οοεβ, while being YCl = Yl;
(c) moving the touch trigger probe (1) in a direction (Y) perpendicular to the first checking direction (Del), of a quantity d = (2r + ΤΗη)3θηβ, to such a coordinate value (YC2), corresponding to a second checking direction (Dc2), that a contact between the feeler (7) and the second surface (S2) can take place at a second point (P2) that is substantially aligned with the first point (PI) along the perpendicular direction (Do) , wherein 2r is the nominal diameter of the feeler (7) and THn is the nominal distance between said first surface (SI) and second surface (S2); (d) during a movement of the feeler (7) along the second checking direction (Dc2), acquiring a position value (X2,Y2) relative to the contact of the feeler (7) at a second point (P2) of the second surface (S2) when the touch signal is provided by the sensor (5) ;
(e) calculating a second position of the center (XC2,YC2) of the feeler (7) by means of the formula XC2 = X2 - Κρ/οοεβ, while being YC2 = Y2 = YCl - d; and
(f) calculating said distance (TH) between said first surface (SI) and second surface (S2) by means of the formula :
TH = sqr [ (XC1 - XC2 ) 2 + (YCl - YC2 ) 2 ] - 2r.
7. Method according to claim 5, for checking the distance (TH) between a first surface (SI) and a second surface (S2) of one or more teeth (T) of a gear or toothed wheel, the method including the following steps:
(a) during a movement of the feeler (7) along a first checking direction (Del), acquiring a position value (XI, Yl) relative to the contact of the feeler (7) at a first point (PI) of the first surface (SI) when the touch signal is provided by the sensor (5) ;
(b) detecting a first position of the center (XC1,YC1) of the feeler (7) by means of the formula XC1 = XI - Κρ/οοεβ, while being YCl = Yl;
(c) moving the touch trigger probe (1) in a direction (Y) perpendicular to the first checking direction (Del), to such a coordinate value (Y2a) , corresponding to a second checking direction (Dc2), that a contact between the feeler (7) and the second surface (S2) can take place at a second point (P2a) that is roughly opposed to the first point (PI);
(d) during a movement of the feeler (7) along the second checking direction (Dc2a) , acquiring a position value (X2a,Y2a) relative to the contact of the feeler (7) at a second point (P2a) of the second surface (S2) when the touch signal is provided by the sensor (5) ;
(e) detecting a second position of the center (XC2a,YC2a) of the feeler (7) by means of the formula XC2a = X2a - Κρ/οοεβ, while being YC2a = Y2a;
(f) calculating a centers distance (CC) between said first and second positions of the centers by means of the formula
CC = sqr [ (XC1 - XC2a) 2 + (YCl - YC2a)2];
(g) calculating a component (CCo) of the centers distance (CC) along the perpendicular direction (Do) perpendicular to said first surface (SI) and second surface (S2) by means of the formula
CCo = CC cos ( - β)
wherein a is the inclination of the straight line on which the centers distance (CC) lies with respect to the checking directions that can be calculated by means of the formula
a = arc tan [ (YCl - YC2a) / (XC1 - XC2a) ] ; and
(h) calculating said distance (TH) between said first surface (SI) and second surface (S2) by means of the formula :
TH = CCo - 2r
wherein 2r is the nominal diameter of the feeler (7) .
8. Method according to claim 6 or claim 7, for checking the thickness (TH) of one tooth (T) of a helical gear.
9. Method according to claim 6 or claim 7, for carrying out a span or Wildhaber measurement on two or more teeth of a helical gear.
PCT/EP2015/059494 2014-05-02 2015-04-30 Apparatus and method for checking the position and/or dimensions of a workpiece WO2015166035A1 (en)

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EP3228973A1 (en) * 2016-04-06 2017-10-11 Jtekt Corporation Gear measurement method and gear measurement apparatus
JP2017191087A (en) * 2016-04-06 2017-10-19 株式会社ジェイテクト Gear measuring method and measuring apparatus
DE202016005708U1 (en) 2016-09-19 2017-12-21 PREMETEC Automation GmbH Gear measuring device
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CN110487155A (en) * 2019-08-02 2019-11-22 西安工业大学 The acquisition methods of linear array gauge head and contact straight spur gear flank of tooth point cloud

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EP3228973A1 (en) * 2016-04-06 2017-10-11 Jtekt Corporation Gear measurement method and gear measurement apparatus
JP2017191087A (en) * 2016-04-06 2017-10-19 株式会社ジェイテクト Gear measuring method and measuring apparatus
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