V-groove shape measuring method and apparatus by using rotary table

• US 6,460,261 B1
• Filed: 11/16/2000
• Issued: 10/08/2002
• Est. Priority Date: 11/18/1999
• Status: Expired due to Term

• Current Assignee: Mitutoyo Corporation
• Original Assignee: Mitutoyo Corporation
• Inventors: Noda, Takashi, Deguchi, Hiromi, Ogura, Katsuyuki
• Primary Examiner(s): Gutierrez, Diego
• Assistant Examiner(s): Jagan, Mirellys
• Application Number:
  US09/713,217
• Time in Patent Office: 691 Days
• Field of Search: 335/017, 335/011.1, 335/011.4, 335/011.5, 331/99.R, 331/99.B, 335/03
• US Class Current: 33/503
• CPC Class Codes: G01B 5/241 for measuring conicity
• CPC Class Codes: G05B 19/401 characterised by control arrangements for measuring, e.g. calibration and initialisation, measuring workpiece for machining purposes G05B19/19 takes precedence
• CPC Class Codes: G05B 2219/4707 Trace groove always at bottom of groove

Abstract

By combining measuring element direction constant control, rotary table radius constant scanning control, and two-flank contact control, V-groove rotary table scanning control is performed to cause the measuring element of the scanning probe to contact always with two flanks composing the V-groove of the object to be measured, so that it is possible to measure accurately the characteristic values such as pitch deviation and axial runout of side face of male threads set up and fixed on a rotary table or screw hole of the object put on the rotary table.

Claims

1. A measuring method of V-groove shape for scanning and measuring a V-groove of an object to be measured by using a scanning probe for measuring position, while rotating the object by a rotary table, with the object having a spiral V-groove fixed on said rotary table, comprising:

controlling a measuring element direction by aiming at keeping constant a vector projected on a table plane of the rotary table of a direction vector from origin of the object to the measuring element of the scanning probe as seen from a machine coordinate system;

controlling a rotary table radius constant scanning of which a confinement plane is a cylindrical plane; and

controlling a two-flank contact scanning for causing said measuring element to contact with two flanks for composing said V-groove,

wherein a V-groove rotary table scanning control is performed while keeping said measuring element always in contact with the two flanks for composing the V-groove.

2. The measuring method of V-groove shape of claim 1,

wherein said V-groove rotary table scanning control is realized by:

sampling a position vector X of said scanning probe, its displacement amount Δ

X, and rotational angle θ

of the rotary table,

calculating an approach reverse direction vector Qu in a direction vertical to the axial center of the object from the rotational angle θ

of said rotary table,

calculating a speed vector of the probe while the rotary table is stopped at the rotational angle θ

,

calculating an angular velocity ω

w of the rotary table by speed vector V of the probe as seen from the axial center of the object,

adjusting advance or retardation from a target value of the rotational angle θ

of the table due to control error from a configuration of the table rotational angle θ and

the probe position X, determining a correction angular velocity Δ

ω

, and correcting the angular velocity ω

w from this Δ

ω

,

calculating a speed vector Vt following up movement of the correction angular velocity Δ

ω

at the probe position X and the table rotational angle θ

, and

calculating a vector sum Vf(=V+Vt) of the follow-up speed vector Vt and probe speed vector V to obtain a probe speed command, and correcting the angular velocity Δ

w by the correction angular velocity Δ

ω

to obtain value ω

t(=−

ω

w+Δ

ω

) as a speed command of the rotary table.

3. The measuring method of V-groove shape of claim 2,

wherein said speed vector V of the probe is sum of at least a basic speed vector Vo showing basic running direction of the scanning probe, a displacement correction vector Ve for keeping constant displacement of the scanning probe, and a two-flank contact vector Vh for causing the measuring element to contact with two flanks of the V-groove.

4. The measuring method of V-groove shape of claim 3,

wherein a radius correction vector Vr for keeping radius constant is added to the sum to obtain the speed vector V of said probe.

5. The measuring method of V-groove shape of claim 1,

wherein it is regarded as an error when two-flank contact is not maintained during said two-flank contact scanning control.

6. The measuring method of V-groove shape of claim 5,

wherein it is judged that the two-flank contact is not maintained when an angle α

formed by the approach reverse direction vector Qu and a vector Es projecting a probe normal vector Eu on a plane formed by the approach reverse direction vector Qu in reverse direction of approach direction corresponding to the object of the scanning probe and vector gθ

corresponding to axial center of the object becomes larger than a specified value.

7. The measuring method of V-groove shape of claim 1,

wherein an approach process is conducted for causing the measuring element of the scanning probe to contact with the two flanks composing the V-groove of the object before starting said V-groove rotary table scanning control.

8. The measuring method of V-groove shape of claim 7,

wherein said approach process is conducted by

moving the object and the scanning probe relatively by a relative speed vector V obtained by sum of a displacement correction vector Ve for keeping constant the displacement of the scanning probe, and a two-flank contact vector Vh for causing the measuring element to contact with the two flanks of the V-groove, and

stopping the probe by judging that the two flanks are brought into contact when an angle α

formed by an approach reverse direction vector Qu and a vector Es projecting a probe normal vector Eu on a plane formed by the approach reverse direction vector Qu in reverse direction of approach direction corresponding to the object of the scanning probe and vector gθ

corresponding to axial center of the object becomes within a specified value.

9. The measuring method of V-groove shape of claim 2,

wherein an approach process is conducted by

moving the object and the scanning probe relatively by a relative speed vector V obtained by sum of a displacement correction vector Ve for keeping constant the displacement of the scanning probe, and a two-flank contact vector Vh for causing the measuring element to contact with the two flanks of the V-groove, and

stopping the probe by judging that the two flanks are brought into contact when an angle α

formed by an approach reverse direction vector Qu and a vector Es projecting a probe normal vector Eu on a plane formed by the approach reverse direction vector Qu in reverse direction of approach direction corresponding to the object of the scanning probe and vector gθ

corresponding to axial center of the object becomes within a specified value.

10. The measuring method of V-groove shape of claim 6,

wherein when approaching from a direction of a certain axis of the machine coordinate system, other axes are clamped so as not to move in other direction.

11. The measuring method of V-groove shape of claim 1,

wherein measurement is conducted when central axis of the object and central axis of the rotary table are not matched with a specified range.

12. The measuring method of V-groove shape of claim 11,

wherein it is judged that the central axis of the object and the central axis of the rotary table are matched when distance from origin of a work coordinate system having the central axis of the object as third axis to central axis of the rotary table, and angle formed by vector obtained by projecting the third axis of the work coordinate system on the plane including both origin of this work coordinate system and the central axis of the rotary table, and the central axis of the rotary table, both settle within a specified allowable range respectively, and judged that the central axis of the work and the central axis of the rotary table are not matched otherwise.

13. A measuring method of V-groove shape, by fixing an object to be measured forming a spiral V-groove on a rotary table, in the case of scanning measurement of the V-groove by using a scanning probe for measuring position while rotating the rotary table, if the central axis of the object and the central axis of the rotary table are matched within a specified allowable range, comprising:

controlling a two-flank scanning for causing a measuring element of the scanning probe to contact with two flanks composing the V-groove; and

controlling a pitch scanning for moving the measuring element in a central axis direction at a speed determined on the basis of the pitch of the V-groove and the rotating speed of the rotary table,

wherein a V-groove rotary table scanning control, while keeping the measuring element always in contact with the two flanks for composing the V-groove, is executed.

14. The measuring method of V-groove shape of claim 13,

wherein said V-groove rotary table scanning control is executed by:

sampling a position vector V of the scanning probe, its displacement Δ

X, and rotational angle θ

of the rotary table,

calculating an angular velocity ω

of the rotary table so that composite speed of a peripheral speed Vω

(=rω

) produced on basis of distance r from central axis of the rotary table to a position vector X, and speed vector Vz(=GP(2π

/ω

) in the central axis direction of the rotary table produced on basis of a specified screw pitch GP when the rotary table is rotated at the angular velocity ω

to be specified scanning speed V,

calculating a speed vector Vz on basis of this ω

value and the screw pitch GP, and

setting the speed vector Vz as a speed vector command Vt to the scanning probe, and this ω

value as a rotational speed command of the rotary table.

15. The measuring method of V-groove shape of claim 14,

wherein the speed vector command Vt of said probe is sum of the speed vector Vz, and a displacement correction vector Ve for keeping constant the displacement of the scanning probe.

16. A measuring apparatus of V-groove shape comprising:

a rotary table fixing an object to be measured forming a spiral V-groove,

a scanning probe having a measuring element engaged with surface of the object,

a drive mechanism for moving the scanning probe along the surface of the object,

position detecting means for detecting position of the scanning probe, and

control means for controlling moving speed of the scanning probe and rotating speed of the rotary table so that the measuring element may always contact with two flanks for composing the V-groove, wherein the control means performs a measuring element direction constant control aiming at keeping constant a vector projected on a table plane of the rotary table of a direction vector from the origin of the object to the measuring element of the scanning probe as seen from a machine coordinate system.

17. The measuring apparatus of V-groove shape of claim 16,

wherein said control means is designed to control in combination of the measuring element direction constant control, a rotary table radius constant scanning control, and a two-flank contact control.

18. The measuring apparatus of V-groove shape of claim 16,

wherein said control means is designed to control in combination of the two-flank contact control and a pitch scanning control.

19. The measuring apparatus of V-groove shape of claim 16,

wherein plural measuring elements differing in diameter are disposed parallel to the scanning probe, so as to be selected according to size of the V-groove.

20. The measuring apparatus of V-groove shape of claim 16,

wherein said rotary table is assembled into a three-dimensional measuring machine, and its coordinate measuring probe is used as the scanning probe.

21. The measuring apparatus of V-groove shape of claim 16,

wherein a hole is drilled in center of rotation of the rotary table and/or in platen of the three-dimensional measuring machine immediately beneath it, for receiving lower end of a long object.