Method and measuring apparatus for measuring a thread

Abstract

A method for measuring a thread includes moving a contactless distance sensor parallel to an axial direction of the thread, recording a measurement signal corresponding to a distance of the contactless distance sensor to a top of the thread, comparing the measurement signal with a reference value lying between a maximum value and a minimum value of the measurement signal, and determining intersection points of the measurement signal with the reference value. Further steps include combining pairs of intersection points, directly following one another, into measurement value tuples, calculating mean values of the measurement value tuples, and calculating a time-angle resolution from the mean values. In an example embodiment, the thread is for a spindle of a ball screw drive.

Claims

1.-9. (canceled)

10. A method for measuring a thread, comprising: moving a contactless distance sensor parallel to an axial direction of the thread; recording a measurement signal corresponding to a distance of the contactless distance sensor to a top of the thread; comparing the measurement signal with a reference value lying between a maximum value and a minimum value of the measurement signal; determining intersection points of the measurement signal with the reference value; combining a first two intersection points, directly following one another, into a first measurement value tuple; combining a second two intersection points, directly following one another and directly following the first two intersection points, into a second measurement value tuple; calculating a first mean value of the first measurement value tuple; calculating a second mean value of the second measurement value tuple; and calculating a time-angle resolution from the first mean value and the second mean value.

11. The method of claim 10, wherein the thread is for a spindle of a ball screw drive.

12. The method of claim 10, wherein the measurement signal is determined as a function of a measurement time from a start time or as a function of an axial displacement from a start location.

13. The method of claim 10, further comprising: combining n pairs of consecutive intersection points into n measurement value tuples; calculating n mean values from the n measurement value tuples; and calculating the time-angle resolution from the n mean values.

14. The method of claim 10, wherein each of the first measurement value tuple and the second measurement value tuple comprises: a first intersection point associated with a rising flank of a thread pitch; and a second intersection point associated with a falling flank of a subsequent thread pitch.

15. The method of claim 10, wherein the step of recording a measurement signal is triggered by a trigger, the trigger being fixed in a longitudinal direction of the thread.

16. The method of claim 10, further comprising calculating an angular displacement of the thread in a circumferential direction relative to a reference angular position of a reference curve of a reference thread from an offset of the first mean value or the second mean value relative to a reference mean value of the reference curve.

17. The method of claim 10, further comprising determining a travel speed or a travel path or a travel time of the contactless distance sensor by calculating a thread pitch of the thread from: a distance between the first mean value and the second mean value; or an average of n−1 distances between n mean values calculated by: combining n pairs of consecutive intersection points into n measurement value tuples; and calculating the n mean values from the n measurement value tuples.

18. The method of claim 10 further comprising measuring a thread of a spindle of a ball screw drive.

19. A measuring apparatus for implementing the method of claim 10, comprising: a holding device for holding the thread; the contactless distance sensor movable parallel to the axial direction of the thread; and an evaluation device for evaluating the measurement signal using the method of claim 10.

20. The measuring apparatus of claim 19, where the thread is for a spindle of a ball screw drive.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In the following, the disclosure is explained by way of example with reference to the attached drawings showing exemplary embodiments. The features shown below can represent an aspect of the disclosure both individually and in combination, wherein:

[0022] the FIGURE shows a schematic diagram of measurement curves obtained with a method for measuring a thread.

DETAILED DESCRIPTION

[0023] The diagram shown in the FIGURE shows the measurement value of a contactless distance sensor representing a voltage 10 in Volts as a function of a measurement time 12 in seconds. The measurement values of the distance sensor result in a measurement curve 14, which essentially corresponds to the course of a thread to be measured along an axial line. The measurement curve 14 intersects a reference value 16, which lies almost arbitrarily between a maximum value and a minimum value of the measurement curve 14. The measurement curve 14 intersects the reference value 16 with a rising flank of a thread pitch with a positive lead in a first intersection point F.sub.S and with a falling flank of the thread pitch with a negative lead in a second intersection point F.sub.F. These two intersection points F.sub.S and F.sub.F form a measurement value tuple from which a mean value M.sub.n is formed, for example according to

[00001]$M_n=\frac{F_F\left(n+1\right)-F_S\left(n\right)}{2}+F_S\left(n\right)$

where n is the nth considered thread pitch of the thread. Given a total number of N thread pitches considered, which follow one another in the axial direction, a time-angle resolution ZW of

[00002]$Z.Math..Math.W=\frac{1}{N-1}.Math.\underset{n=1}{\overset{N-1}{.Math.}}.Math.\frac{M_{n+1}-M_n}{360.Math.°}$

results for a single thread when averaging over the thread pitches considered.

[0024] A thread lead 18 can be determined from the distance between two subsequent mean values, for example M.sub.n and M.sub.n+1, in particular for a single thread. For better clarity, this is shown in an exemplary manner in the diagram shown with the mean values M.sub.n−1 and M.sub.n−2. In addition, the measurement curve 14 can be compared with a reference curve 20. If the thread is rotated by an angular amount in relation to the angular position of the thread of the reference curve 20, there results a temporal phase difference t.sub.s between the mean value MP.sub.n of the measurement curve 14 and the corresponding mean value MB.sub.n of the reference curve 20, according to

t.sub.s=t(MB.sub.n)−t(MP.sub.n).

[0025] From this, an angular displacement Δφ between the angular position of the thread of the measurement curve 14 and the angular position of the thread of the reference curve 20 in the circumferential direction can be determined, according to

Δφ=t.sub.s.Math.ZW.

REFERENCE NUMERALS

[0026] 10 Voltage [0027] 12 Measurement time [0028] 14 Measurement curve [0029] 16 Reference value [0030] 18 Thread lead [0031] 20 Reference curve [0032] ZW Time-angle resolution [0033] F.sub.S Intersection rising flank [0034] F.sub.F Intersection falling flank [0035] M.sub.n Mean value [0036] MP.sub.n Mean value of the measurement curve [0037] MB.sub.n Mean value of the reference curve [0038] t.sub.s Phase difference [0039] Δφ Angular displacement