Needle Tip Quality Inspection

Introduction

The standards of needles for medical application are very high. A large amount of these needles, particularly with a special shape, are produced with a spark-erosion machine that can produce any shape.
These spark-erosion machines are in principle very precise. Nevertheless, small errors or damages occur during or after the production process.
Therefor a quality control is in order. Currently this is still done by hand.
An automated inspection and selection system will not only save on costs, but it can objectively guarantee the right quality.

This publication gives the following results of a needle quality measurement, executed by vision:
1. contour measurements
2. surface quality measurement

Contour Measurements

1. Good cut surface profile

The first image is an example of a good cut surface profile. The purple points in the image indicates the measured contour points of the cut surface.
The cut surface isn't straight but curved.
The graphical representation on the left displays the calculated distance ('width') between the cut surface and the bottom of the needle.
The white line in the graph represents a linear fit and the red line a parobolic fit of the measured points. JAIMS Measured curve good profile JAIMS Needle side view good profile
The small spike in the graphical representation is of a dust particle at the tip of the needle.

Measurements are displayed in pixels, with 1 pixel representing 3 micrometer vertically and 5 micrometer horizontally. (dust particle is 36 micron high and 60 micron wide)

JAIMS Measured curve bent tip JAIMS Needle side view bent tip

2. Rejection cut surface profile

Here the tip of the needle is crooked (damage = rejection).
The upper graph shows both the bent tip as well as a small dust particle.
It shows also the linear and parabolic fit of the measured points.
The lower graph shows the difference between the measured points and the linear and parabolic fit.
The crooked tip is well detectable.
The curve of the tip is more than 150 micron high and 150 micron wide. The dust particle is 24 micron high.

3. Rejection Cut Surface Profile, Poorly Produced

JAIMS Measured curve lump JAIMS Needle side view lump This needle has a poorly produced cut surface with a 'lump' with a height of 50 micron and a width of 375 micron.
The very small spikes are dust particles.
The bottom graph displays the difference between the measured contour points of the cut surface, the fitted linear curve (white) and the parabolic curve (red).

Surface Quality Measurement

Through application of the right lighting damages like a bright scratch become apparent (image left).
Damages can be detected in multiple ways:

JAIMS Needle top view scratch JAIMS Needle top view scratch detected

1. Local intensity detection,

gives the result displayed in image on the right.
The small red dots indicate detection noise and can be filtered out.
This results in a clear damage, of which we can determine the length, width and damage area. JAIMS Measured lump dynamic contrast JAIMS Needle top view lump

2. Dynamic contrast measurements,

like applied on the needle with the poorly produced cut surface, image on the left.
After detection, the length, width and area of the damage can be determined.
Results are shown in image on the right.

The dynamic contrast measurement also detects the damaged tip. JAIMS Needle top view bent tip
If the damage exceeds the rejection limit, the product is rejected.
An extra contour measurement calculates the deviation with regard to an ellipse.
This gives very accurate geometrical results, as displayed with the bent needle tip in image left.
For more detailed information about Needle Tip Quality Inspection download the pdf in English: Needle Tip Quality Inspection.pdf or in Dutch: Naaldpunt Kwaliteitsinspectie.pdf