1. Non-Contact Inspection of Internal Threads of Machined Parts
E. Hong | H. Zhang | R. Katz | J.S. Agapiou
Presentation by Guy Pinkas & Jonathan Avidan

2. Terminology Non-contact inspection Internal threads Laser sensor
Image processing

3. Introduction Importance of threaded joints (50% of all joints)
Common defects (Missing thread crest, Scratches or defects, Discontinuities)
Primary methods for threads metrology and inspection
Contact gauges (Go / No-Go)
CMM (Coordinate Measurement Machine)
Nondestructive techniques present some challenges
Suggestion of 2 new methods
“Optimet” conoprobe sensor (laser sensor)
CCD camera and an illumination system

4. Angular Position of Internal Thread
First challenge – Spark plug
Locating the starting point of the internal thread
The technique
Thread is scanned in 4 internal lines
The location is determined by comparing the 4 values
The largest and smallest measured distances must be neighbors
Can be extended by dividing the quadrants
The technique provides information about the angular position and direction of the thread

5. Standard Thread Profile
Main geometrical parameters
Pitch [ p ]
Minor Diameter [ DMIN ]
Pitch Diameter [ DP ]
Major Diameter [ DMAJ ]
Thread Height [ H ]
Flank Angle
Helix Angle
Parameters determination
Minimum of 2 profile laser scan
Opposite 180°
More Scans will increase accuracy but will take more time

6. Surface Inspection – Laser Sensor
Using the Optimet conoprobe laser sensor for measurements
Internal cylindrical surface check adaptation
Designed and built a unique motorized periscope
Designed mechanically and geometrically for circular scan
Combined motion – linear and rotation

7. Surface Inspection – CCD Camera
Use line scan to acquire a high quality image (of the surface)
Use sight pipe optical device with a conical mirror - 360° view
Scans annular sections & Unwrapping the scanned images
Combine the sectors to flat image and inspect with algorithm
Method can also use to inspect surface defects

8. Experimental Setup Laser scan Internal thread inspection
3 linear motion stages & rotary stage
Internal thread inspection
3 linear motion stages
2 tilt adjustment stages
CCD camera
Optical lenses
Ring led light
Set of sight pipes (for each diameter)

9. Experimental Results Detection of a thread starting point
Inspection on M12x1.25 nut
PS’ depicts the corrected PS after self-calibration
From the results : PS’1 > PS’2 > PS’3 > PS’4
Starting point located in quadrant 4
The helix is a clockwise rotation
270°
180°
90° 0°
0.44
1.082
2.379
2.531
PS [mm]
1.384
1.942
2.288
PS’ [mm]

10. Experimental Results Internal thread dimensional measurement Standard
Max
Min
Average
Parameter
1.251
Pitch
12.36 12
12.108
Major Diameter
10.912
10.647
10.863
Minor Diameter

11. Conclusion
2 new methods for non-contact inspection of internal threads
Laser sensor and a motorized periscope
CCD camera with sight pump
The methods functionality
Find angular position of internal thread starting point
Reduce measuring time and cost
Measure long internal threads of small diameter
Allow inspection of 100% of threads used in safety related parts
Detect internal flaws found on threads surfaces

12. Questions ?