Syringe manufacturers need to maintain high levels of quality in order to ensure the safety of patients and caregivers while at the same time maximizing productivity to deliver their product at a competitive price. AVTEX (Burlington, CT, USA; www.avtex.net) Machine Vision Inspection Stations were customized specifically for a two-machine syringe assembly process coupled with a packaging system built by Arthur G. Russell Co. (AGR; Bristol, CT, USA; www.arthurgrussell.com) to meet both goals. The machine-vision system performs a series of inspection operations, such as ensuring the presence and location of components, as quickly as 50 ms.
"The key to maintaining AVTEX's Inspection Station's accuracy at ultrahigh levels of speed is incorporating Cognex VisionPro software, which includes vision tools with the intelligence to ignore noncritical variations in appearance while focusing on the critical features that determine a product's acceptability," says Mark Granahan, president of AVTEX.
Established in 1995, AVTEX is dedicated to machine vision and is headquartered near Hartford, CT, with an engineering branch in Bristol, CT, at AGR. AVTEX's clients include North American and European manufacturers and machine assemblers in industries ranging from consumer products to medical, automotive, aerospace, and electronics.
Since its founding in 1945, AGR has been producing automatic assembly equipment (see videos on factory automation). AGR has built hundreds of large-scale machines and thousands of precision feed systems for the assembly of medical products such as syringes and blood collection tubes. The company has experience with high-speed assembly of all types of medical products, as well as a thorough understanding of the US Food & Drug Administration requirements for medical product assembly.
"We used Cognex VisionPro software to develop six machine-vision inspection stations for this machine," says David Baker, AVTEX engineer. The VisionPro tool library offers a range of tools that support a variety of machine-vision applications.
Machine produces 480 syringes per minute
AGR's process to produce syringes required two machines and 17 individual stations. The first machine indexes every 2 s and processes 16 syringes during each cycle for a total production rate of 480 syringes per minute. The needles, or cannula, are loaded into the first station of the machine. The needles are then picked up from a hopper by a vacuum gripper and the point end is inserted into a wheel. At the bottom of the wheel, needles are transferred to a belt to be presented to a vacuum pickup head. At Station #2, the needles are picked up and rotated 90° and inserted into plastic hubs. Each hub includes a protector that is applied to the needle after it has been used to prevent accidents. Adhesive is applied to each hub-needle assembly in Station #3 and cured with ultraviolet light in Station #4.
The needles could appear in the pallet at the first station of the machine at any angle. A machine-vision system at Station #5 determines the angle of the needle. This operation occurs during the index of the machine, which constitutes 660 ms of the cycle, leaving only 41 ms for each needle to be inspected. AVTEX engineers created a custom lens light and selected a Sony (Park Ridge, NJ, USA; www.sony.com/videocameras) XC-HR50 camera and Cognex (Natick, MA, USA; www.cognex.com) VisionPro software to perform this inspection operation. The VisionPro PatMax pattern-matching tool was used to locate the part and report its orientation to the machine control system.
Three-step geometric measurement process
The programmers provide examples of good needles for training models used by the PatMax software from Cognex. PatMax uses geometric information in place of pixel grid-based correlation. For example, it interprets a square as four line segments and a football as two arcs. It does this by applying a three-step geometric measurement process to an object. PatMax identifies and isolates the key individual features within an object image and measures characteristics such as shape, dimensions, angle, arcs, and shading. It then correlates the spatial relationships between the key features of the trained image to the runtime image, encompassing both distance and relative angle. By analyzing the geometric information from both the features and spatial relationships, PatMax is able to determine the object's position without regard to the object's angle, size, or appearance.
Station #6 uses a gripper arm driven by a servo motor to rotate the needle into the proper orientation for subsequent processing steps. This servo-driven assembly provides accurate, high-speed handling of the needles. Station #7 is another machine-vision station that verifies the needle orientation using the same camera and AVTEX software as Station #5. Stations #5 and #7 are run on the same personal computer.
Station #8 uses VisionPro software to inspect the assembly to ensure that the hub has been securely fastened to the needle. Two XC-HR50 cameras look at the assembly from the top and side views. The software analyzes both images to determine whether or not a sufficient amount of adhesive has been applied in the right location. The two cameras are also controlled by the same personal computer that controls stations #5 and #7.
Blob tool needle check
Station #8 uses two XC-HR50 cameras that are perpendicular to each other and the VisionPro edge tool to measure the angle of the needle relative to the hub. At this point, the needle is moving on tracks with the needle bevel facing in the direction of motion. At Station #9, another vision application backlights the pointed tip of the needle and checks to make sure it is intact. This station uses VisionPro's grayscale blob tool to inspect the height and angle of needle tip to check for problems such as the tip being folded over. The grayscale blob tool provides repeatable measurements of connectivity, area, size, and shape of objects.
At Station #10, a servo-driven gripper inserts shields over the tips of syringes that have passed all of the previous inspections. Station #11 is an unloading station in which a vacuum-operated gripper head picks up the syringes that have passed inspection and puts them on a conveyor. The gripper head has 16 pockets; individual pockets can be turned on and off depending on the inspection results.
The conveyor carries the syringes to a second machine that indexes every second. Station #1 of this machine is used for loading the needle/hub assembly into the machine from the conveyor. Station #2 uses a gripper driven by an AC motor to screw the syringe onto the needle-hub assembly. The motor has a clutch that breaks away once the proper torque limit is reached. In Station #3, a gripper picks up the syringe and places it into a plastic blister pack that holds 10 units.
Inspecting the packaging
Station #4 is an inspection station where two XC-HR70 cameras look at the blister pack. These cameras use the PatMax pattern-matching tool to check that each pocket holds a syringe and that all of the major components of the syringe—such as needle, hub, shield, and protector—are present. "We use the PatMax tool for this station because the syringe could be located anywhere within the blister-pack pocket, and PatMax is very good at locating things when you do not know in advance where they will be," Granahan says. This inspection station works during the stationary part of the cycle, which occupies approximately 660 ms, but the actual inspection operation only takes about 50–60 ms.
Station #5 applies a paper backing to the blister packs that have passed inspection. Station #6 separates the packages that passed from those that failed the inspection. Only packages that pass inspection are loaded into boxes. Those that fail are placed into a bad parts bin for reworking.
"These machines provide the customer with the ability to produce syringes at a rate of approximately twice the level that was possible in the past," and with 2X accuracy, notes Granahan. "A key to their success is the use of machine-vision systems that operate at the high production rates of the machines while providing 100% inspection that ensures the quality of every unit."
-- Posted by Carrie Meadows, Vision Systems Design, www.vision-systems.com