Vision-guided robotics check for particles in drug vials.
Machine vision has been most commonly used in semiconductor, electronics, automotive, and general manufacturing applications. Recently, the stringent quality demanded of production processes by pharmaceutical companies has created rapidly growing opportunities for vision and automation-but only for the most innovative of machine-vision system integrators.
Before drugs are sold, they must be checked for the presence of foreign particles. To accomplish this, Gerald Budd, president of Phoenix Imaging (Livonia, MI) and his colleagues have now developed a robotic-based vision system called ParticleScope, which can automatically load and unload products onto a test stand, and inspect for particles in a fraction of the time required by human operators.
Budd, who is a physicist with a background in optics and machine vision, and Jules Knapp, a pharmaceutical industry expert in the field of particle inspection, teamed up in 1996 to begin tackling this very difficult application. “In the design of the system,” says Budd, “a number of important physical properties characterizing the fluid dynamics of the system and the motion of particles within the fluid needed to be considered.” These properties relate to the vessel size and shape, the fluid viscosity and surface tension, and the fluid fill volume, as well as the size, shape, and density of any particles that may be present. By tabulating all of these properties into a single matrix, Phoenix Imaging developed a specific velocity motion profile for numerous products. “When each vial is rotated,” says Budd, “larger particles are spun via centripetal force to the outside of the vial while smaller particles (and those with less mass) will remain in the vial center. Thus, by properly controlling the velocity, it is possible to anticipate particle position and accurately measure the particle size.”
Fluid in Motion
In the ParticleScope design, many illumination, imaging, motion, and robotics challenges had to be overcome. “To ideally illuminate the vial as it rotates,” says Budd, “you would need to uniformly light the sample from all sides. However, we developed a custom U-shaped LED light module using more than 1000 630-nm red LEDs from Nichia (Tokushima, Japan).” Using a custom-built current controller, light intensity is controlled from the PC. “Thus,” says Budd, “low opacity particles (such as fibers) can be illuminated more effectively using low-light levels while heavy (optically dense) particles can be lit with a brighter, more intense light.”
A large depth of field (DOF) is required to image particles within each vial. The developers used a relatively long 100-mm-focal-length lens from Kowa (Tokyo, Japan) and folded optics to increase the object-to-camera distance and thus the depth of field on the object side. Budd says they could have used other methods, including wavefront-encoding techniques from CDM Optics (now part of Omnivision Technologies; Sunnyvale, CA), or by the use of DOF enhancers such as those used by Fluid Imaging (Edgecomb, ME). However, both methods would have been more expensive to implement.
In operation, reflected images from the vials are transmitted through the folded-optic assembly and imaged by a 1300 × 1030-pixel Camera Link camera from JAI PulNix (San Jose, CA). Interfaced to a frame grabber from Epix (Buffalo Grove, IL), images are directly transferred to the host PC memory for processing. A small VP Series robot from Denso Robotics (Tokyo, Japan) is mounted inverted above the laboratory unit.
In the past, human inspectors performed a statistical analysis on thousands of vials before a 1% confidence level in the batch quality could be determined. Today, anticancer medications are manufactured in expensive clinical trial batches of less than 3000 vials, making it nearly impossible to approach the task with human inspectors.
“Worse,” says Budd, “some drugs may have a shelf life of just a few days or even a few hours and testing needs to be accomplished very rapidly.” The ParticleScope eliminates the need for time-consuming statistical measurements. The system is currently being reviewed by several pharmaceutical-equipment builders in an effort to implement the technology in high-speed (150 to 300 vials per minute) production machines. The opportunities for such innovative, vision-based pharmaceutical manufacturing equipment are many, but clearly they are not simple to develop.
CONARD HOLTON is editor in chief of Vision Systems Design; e-mail: [email protected].