TRANSMITTED LIGHT (STATIC DIVISION) AUTOMATED INSPECTION SYSTEMS

To overcome the limitations inherent with camera-based systems based on light reflected from particles in solution, an inspection system based on light transmitted through the solution was developed. Any particles in the solution block a portion of the transmitted light, casting a shadow that is detected by an array of small, light-receiving diodes. Acceptance or rejection is therefore based only the size of the particulate, not on any other factor such as its reflective strength. Additionally, by analyzing only the change in light intensity caused by moving particles, the signals can be distinguished from static light reduction caused by stationary objects such as scratches, dirt, and printing on the container surface, significantly decreasing the rejection of qualified products (false rejects). Unlike camera-based systems that capture, process and compare images, the Static Division system reads voltage fluctuations in real time.

Named "Static Division" (SD) for its ability to differentiate static from moving objects, the technology has revolutionized the inspection of particulates, with over 900 systems installed in more than 50 countries since its introduction in 1975.

A moving particle blocks light and casts a shadow, which creates a voltage signal proportionate to the size of the particle, independent of shape, color or composition. During operation, a direct halogen light source passes light through a container that is spun at high speeds just before reaching the inspection stage, so that any particles present are set in motion. Lenses focus the light beam down the centerline of the container and onto the sensor array. Since the shadow cast by an individual particle represents a significant portion of a single diode's area, the presence or absence of a particle significantly varies the amount of light received by the diode and, in turn, the accuracy of its detection

The light transmission SD (Static Division) system consists of a light projector that transmits a high intensity light beam perpendicular to the container. A stack of small sensors (diode array) is located at the other side of the container. An image of any particles within the solution that interrupt the light beam is transposed on the small sensor surface, and the instantaneous change in the light intensity is measured. Thus, by analyzing only the change in light intensity caused by moving particles, the signals can be distinguished from static objects as noted. The size of the particle determines signal level, making equal detection capability possible for colored particles having low reflectivity. The SD system was able to improve inspection performance drastically compared to manual inspection, and with repeatable results. Another advantage of the SD system was that fewer parameter settings for inspection were needed, simplifying maintenance and calibration while preserving inspection capability.

Static Division System Operation

The container to be inspected is rotated by the spinning unit between 1000 and 5000 RPM before inspection, and is suddenly stopped by a brake just before inspection. At that time, although the container itself is stationary, the liquid inside the container continues rotating because of inertia. This phenomenon is utilized to float insoluble foreign particles existing in the container. The image of a floating foreign particle is projected onto the SD head by transmitted light illumination. The moment the image of the particle passes through the sensor surface, the quantity of light received by the affected bits varies. The presence of a foreign particle is sensed by detecting variations in the quantity of light received by the sensor units (shadows) and the change in DC voltage is extracted for comparison with the detection sensitivity level. If the DC voltage is greater than the detection sensitivity level, it is picked up as a foreign particle signal.

The container to be inspected is rotated by the spinning mechanism before inspection, then stopped prior to inspection. In addition to setting the particles into motion within a stationary container, a pre-spin station serves to remove bubbles that would otherwise cause false rejects.

Although the quantity of light received by the bits on which stains or printings on the container are projected is also reduced, the detector only perceives the variation of light intensity caused by the moving particles and coverts those moving shadows to an AC electrical signal in real time. Since the markings on the outside of the container do not move, their cast shadows are stationary and converted to a DC electrical signal which is filtered out of the inspection process, minimizing false rejects.

Static Division Sensor

The image of the container is projected onto the photo-detector (SD head) by the projector section (light source and projection lens) and the Selfoc (self focusing) lens. The high-resolution SD head consists of vertically stacked photodiodes (having the same surface area as the lens) that convert shadows cast by particles into electrical signals. Performance of the photodiodes does not change over time, and no adjustments are needed. Each contains mutually independent circuits incorporated for real-time processing. The inspection view can be adjusted by setting the number of bits according to the container fill level.

Since the SD system relies on transmitted light, which is unaffected by external light, it can be installed in virtually any workroom with no effect on detection performance.

The Static Division sensor can detect glass particles, rubber particles, white fibers, black particles, dirt, hair, dust, lint and other particles in solution contained in vials, ampoules, syringes and cartridges that are either molded or tubular.

Sensing Capabilities

The baseline of inspection is human detection, due to the Pharmacopoeia requirement that foreign matter visible to the human eye should not be present. A benchmark is that a human inspector can detect a 50-micron size particle roughly 50% of the time. A typical visible particle can be detected by the SD system at a level, which is equal or better than human inspection.

The key to detection, however, is to not reject good product. Due to the linear response based on particle size, the Static Division sensor allows the user to more closely approach the ideal detection curve of 100% detection of faulty and 100% passing of good than a human inspection process.

The SD System's Foreign Particulate Detection Characteristic Curve provides a narrow gray zone as detection is based on particle size, and consistent results are achieved with minimal false rejects. The curve should be as sharp as possible, close to the ideal regardless of the sensitivity level selected.
 

CAMERA SYSTEMS USED FOR PARTICLE DETECTION

Static Division (SD) systems currently inspect the majority of parenteral products in clear solutions worldwide, primarily due to their low false reject rates and ease of set up. High-speed cameras are also widely employed, independent of or in conjunction with SD systems, for floating particle inspection (particularly for high viscosity solutions) as well as non-moving particles.

Floating particle	Sinking particle

Conveyance of Containers

Central to mechanical automation capability is an oscillating drive unit that provides continuous stable motion for container and inspection system transport. The design and construction of the oscillating drive prevents vibration to minimize interference with the inspection process, and provide more than 400 milliseconds of inspection time per container.

The maximum body diameter of each size container is the limitation according to the model selected. The model of machine is chosen based on this important dimension, as well as the total height. This is critical is because of its influence on the pitch of the inspection table which influences inspection time.

Containers filled with injectables are conveyed by the starwheel onto the rotating inspection table, on which each container is spun at a high speed and stopped immediately prior to entering the inspection area, and inspected twice, while the solution inside is still rotating. If any particulate is present, it blocks the light. The sensor perceives the light variation caused by the particulate and judges the container acceptable or faulty in accordance with the preset sensitivity level.

Smooth handling of containers is essential for proper detection.

Also see CAMERA-BASED SYSTEMS FOR PARTICULATE AND COSMETIC INSPECTION