Method of monitoring and controlling a screwing process

• US 6,581,472 B2
• Filed: 08/29/2001
• Issued: 06/24/2003
• Est. Priority Date: 08/29/2000
• Status: Expired due to Term

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Schneider, Eckhardt, Herzer, Rüdiger
• Primary Examiner(s): Kwok, Helen
• Assistant Examiner(s): MILLER, ROSE MARY
• Application Number:
  US09/940,437
• Publication Number:
  US 20020023503A1
• Time in Patent Office: 664 Days
• Field of Search: 737/61, 735/97, 735/98
• US Class Current: 73/761
• CPC Class Codes: B25B 23/14 Arrangement of torque limiters or torque indicators in wrenches or screwdrivers couplings for transmitting rotation or clutches F16D; devices for measuring torque per se G01L
• CPC Class Codes: B25B 23/1425 by electrical means
• CPC Class Codes: G01N 2291/02827 Elastic parameters, strength or force
• CPC Class Codes: G01N 2291/02854 Length, thickness
• CPC Class Codes: G01N 2291/044 Internal reflections (echoes), e.g. on walls or defects
• CPC Class Codes: G01N 2291/101 one transducer
• CPC Class Codes: G01N 2291/2626 Wires, bars, rods
• CPC Class Codes: G01N 2291/269 Various geometry objects
• CPC Class Codes: G01N 2291/2691 Bolts, screws, heads
• CPC Class Codes: G01N 29/07 by measuring propagation velocity or propagation time of acoustic waves
• CPC Class Codes: G01N 29/227 related to high pressure, tension or stress conditions
• CPC Class Codes: G01N 29/4436 with a reference signal amplitude comparison G01N29/48

Abstract

In the present method for monitoring and controlling a screwing process in creating a screw connection, ultrasonic pulses are coupled into the screw using a pulse-echo method before and during the tightening of the screw. The time for the pulses to traverse the length of the screw, i.e., the propagation time, is measured. A dependency of the propagation time on the predetermined tension of the screw is calculated from the material specific characteristic values of the screw and the measured propagation time. By comparing the values of a change in propagation time dependent on a parameter of the screw with the values of a change in propagation time dependent on the predetermined tension of the screw, the screwing process can be monitored.

Claims

1. A method for monitoring a screwing process in creating a screw connection with a screw, comprising:

(a) before starting a tightening process of said screw,

coupling at least one first ultrasonic pulse into said screw using a pulse-echo method, starting from a head of said screw, and measuring propagation time of said at least one first ultrasonic pulse for traversal of length of said screw;

calculating at least one value of a change in propagation time of said at least one first ultrasonic pulse as a function of a predetermined tension of said screw, the calculating being of material specific characteristic values of said screw and said propagation time; and

storing the at least one value for the change in propagation time as a function of said predetermined tension to provide stored values;

(b) during said tightening process,

repeatedly coupling second ultrasonic pulses into said screw using a pulse-echo method, starting from the head of said screw, and measuring propagation times of said second ultrasonic pulses for traversal of the length of said screw;

determining at least once a first value of a relationship between a change in propagation time and a change in a screw parameter influencing said predetermined tension of said screw from the propagation times measured of said second ultrasonic pulses;

determining at least one second value of the relationship between a change in propagation time and a change in said predetermined tension of said screw from said stored values; and

comparing said at least one first value with said at least one second value.

2. A method according to claim 1, further comprising influencing said screw parameter to achieve a required predetermined tension in a prescribed process time when deviation of said at least one first value from said at least one second value occurs.

3. A method according to claim 1 or 2, wherein said method indicates a deviation above or below a prescribed value of said at least one first value from said at least one second value.

4. A method according to claim 1 or 2, further comprising discontinuing said tightening process when deviation above or below a prescribed value of said at least one first value from said at least one second value occurs.

5. A method according to claim 1 or 2, further comprising before starting the tightening process, calculating a desired propagation time from a prescribed tension of the screw, said material specific characteristic values of said screw and said propagation time measured;

said propagation time measured being compared with said desired propagation time and upon achieving said desired propagation time, discontinuing said tightening process.

6. A method according to claim 1 or 2, further comprising determining said material specific characteristic values in preliminary tests, said material specific values being dependent on tensile strength class and method of production of said screw.

7. A method according to claim 1 or 2, further comprising determining a material specific non-linear tension-elongation relationship dependent on tensile strength class and method of production of said screw in preliminary tests, and obtaining characteristic values for calculating sound propagation time as a function of predetermined tension of stretch screws tightened beyond their elastic limit.

8. A method according to claim 1, wherein said measuring of said propagation time occurs at least 100 times per second.

9. A method according to claim 1, wherein said coupling is by an ultrasonic probe and said tightening process is by a drive means spindle having a rotating element and a stationary element, and transmission of electric signals to and from said ultrasonic probe occur in a contactless manner between said rotating element and said stationary element.