Camera system for checking lotion bottle cap orientation, for a skincare product manufacturer (FMCG)

How the brief came about

This system uses a camera to inspect lotion bottles in place of inspection by eye at the end of a filling line. This skincare product manufacturer's line runs at up to 120 bottles per minute. At the time, 2 staff inspected and corrected labels by eye at the packing point.

The customer wanted a camera to inspect the front and back labels and to check that the bottle cap faces the right way. Incorrect bottles had to be rejected for correction. Cap inspection was an additional requirement from the customer.

Requirements and constraints

The requirements for this work come from the customer's requirements document, which was written for the complete inspection machine. Our prototype took on only the cap orientation requirement. The main requirements are as follows.

• Work with a filling line running at up to 120 bottles per minute
• Inspect front and back labels: missing labels, skewed labels, incomplete print and scratches
• Check that the flip-top cap faces the right way, with the cap tilted by less than 10 degrees
• Reject incorrect bottles for correction, in place of staff inspecting by eye
• Scope of the prototype test rig: cap orientation tested on the test rig; labels and real line speed must be tested separately

How the prototype decides whether a bottle cap faces the right way

The prototype decides cap orientation by measuring the cap's rotation angle in degrees, then comparing it with the 10-degree criterion from the customer's requirement. The customer's criterion is already a number, so an angle measured in degrees can be compared directly with it, giving a pass or reject result that can be checked repeatedly.

1. 1

   Capture the bottle cap image

   Set up the test rig so that the industrial camera sees the bottle cap from a defined distance and angle.

2. 2

   Process the image

   The Medusa processing unit runs an image processing program to find the position and rotation angle of the cap.

3. 3

   Decide against the criterion

   A cap tilted by less than 10 degrees passes; at 10 degrees or more, the bottle must be rejected.

4. 4

   Display the result

   The inspection result shows on the program screen whether the cap passes or must be rejected.

What we built and tested

We built the test rig, tested it with sample bottles and summarised the full system components. The items are as follows.

• Test rig: industrial camera, Medusa processing unit and an image processing program that measures the rotation angle of the flip-top cap
• Sample inspection results for good and defective caps against the 10-degree criterion, shown on the program screen
• Full system components for a real line: multiple camera sets, lighting and system integration with the filling line

Details of test results on real workpieces

The recorded test results are sample images of good and defective caps against the 10-degree criterion. These images show a pass or reject result on the program screen. The documents do not record numerical test results, so we do not report an accuracy figure.

This result covers the cap orientation requirement on the test rig. For use on a real line, testing must be repeated at line speed, label inspection must be tested separately, and a mechanism for rejecting bottles from the line must be designed.

What we learned

The main lesson from this work is to start from numerical criteria and to have numerical test results before deciding to invest in a full system. The principles we have carried forward are as follows.

• Start testing from numerical requirements. A cap angle that must stay under 10 degrees converts directly into a rule in the program, whereas label defects such as skew or scratches need a numerical criterion agreed for each type before they can be tested.
• Prototype results must be recorded as numbers that can be checked repeatedly. Sample images of good and defective work help to show the direction, but an investment decision needs numerical test results, and testing must be repeated at real line speed before use.
• The camera is only one part of an inspection machine. A full system must include multiple camera sets, lighting, system integration and installation, which a test rig testing a single requirement does not yet cover.

How to apply this approach to your filling line

If your line fills products into bottles and needs cap or label inspection, you can use the same approach as this case: test numerical criteria on real bottles at prototype level first, then assess the full system. What needs adjusting is the camera angle, lighting and criteria when your bottle, cap or label differs from this case.

• Prepare pass/fail criteria agreed by your quality team, such as cap tilt angle or label skew distance.
• Prepare sample bottles, both good and defective, covering every size and cap type you actually produce.
• Prepare line speed information and the camera installation area, to plan repeat testing on site before handover.