As demand for medical devices continues to escalate, so does demand for more automated and efficient manufacturing processes. To ensure product quality control is not compromised, sensors can be used to detect, verify, and inspect medical products right on the manufacturing line. Today's innovative sensor technologies offer manufacturers a plethora of options to integrate sensor inspections into their operations. Selecting the right sensor technologies for each unique application ensures manufacturing lines run more efficiently while offering manufacturers enhanced process control — and consumers, a higher level of quality assurance.

Photoelectric: proven

A photoelectric sensor is one of the most cost-effective and proven methods for object detection in manufacturing processes on the plant floor. Photoelectric sensors detect objects based on how light energy is blocked, transmitted, or reflected by the target objects. The level of contrast between a light and dark condition determines how well sensors can decipher the presence or absence of objects. A common problem occurs with low contrast sensing applications when the target object does not create enough light difference, or signal change, between light and dark conditions. For instance, clear plastic or glass material used in medical products, such as vials, IV bags, and syringes, are usually more challenging to detect since the contrast is very low.

Today, photoelectric sensors tackle these challenges by incorporating sophisticated software algorithms, optical components, and simple configurability. Clear or semitransparent medical products can be detected reliably using a low contrast object detection sensor in the retro-reflective sensing mode. In this mode, the sensor houses the emitter and receiver within the same device and emits its light beam toward a reflector, which is placed opposite the sensor. The sensor is then “taught” the specified reflected light intensity from the reflector. As the clear object is presented between the sensor and the reflector, the light intensity will deviate from the original taught level and signal an output when the switching threshold reached. A sensor optimized for detecting clear objects can detect very small changes in the light intensity of its emitted beam — down to a single-digit percentile — providing the high sensitivity needed to identify low-contrast objects.

Fiber optic: environmental challenges

At times, detecting the product itself is not the challenge, but rather the manufacturing environment. For instance, sterilization is necessary in some medical products prior to final packaging of finishing. This sterilization process occurs in areas that may exceed 140° C — far too high for standard sensors. For these applications, fiber optic sensors offer an alternative and exceptional sensing capability while withstanding challenging environments. Fiber optic sensors use the amplifier to emit and receive light through fiber optic light-guides. These optical fibers are made of either glass or plastic constructed into light bundles. This design enables the light signal to travel through protected fiber optic cable and assemblies to tolerate harsh external environments. High- temperature rated plastic fibers may be used in areas reaching up to 105°C, while high-temperature rated glass fibers can withstand temperatures up to 315°C.

Due to their small size and flexibility, fiber optic assemblies can be shaped to meet the physical and optical requirements of a specific application. This light beam may also be designed so that it is distributed, or fanned, across a two-dimensional area to detect small objects. During the manufacturing of tiny medical products such as implantable components — of which the parts may only be a few millimeters wide — a fiber optic sensor can use these two-dimensional optical arrays to detect the object, then send these results to a counting device. This arrangement allows for efficient non-contact detection of small medical products and confirms the proper number of devices is packaged before shipping. A fiber optic sensor may also be used to confirm ejected parts such as vial stoppers are produced correctly.

Vision: analyzes and interprets

Complex applications require not only “eyes” on the plant floor, but also the ability to interpret the observed conditions. Unlike the photoelectric sensors described above, a vision sensor analyzes and interprets data from an entire field of view, rather than just a single point. A vision sensor acquires an image of the product and, after analyzing it, determines whether the product passes the inspection. The sensor then outputs the results to the manufacturing line's control system, informing it to divert the reject from the production line. This inspection method may be used for assembly verification; feature recognition by color or date/lot code; feature identification by color, size or shape; and location analysis to confirm a product is correctly oriented before it enters the next production stage.

Vision sensors that offer barcode reading tools are especially useful in medical product manufacturing, as this capability is applied to identify product codes, date/lot codes, and other pertinent information on medical products. Along with providing users with the ability to track and trace products during the manufacturing process, it allows end-customers or vendors to track the origins of medical products after they are distributed throughout the supply chain. The same BCR tool facilitates simple identification and grading of barcodes, further ensuring each product can be easily identified after its introduction to the consumer market.

Vision technology has evolved significantly not only through advanced inspection capabilities, but also by making vision sensing easier to use on the factory floor. Advanced features such as an LCD touchscreen display — amature technology in consumer electronics — offers a simple-to-navigate interface that allows even first-time sensor users to set-up a complex inspection with ease. Not only does this significantly reduce the learning curve and installation time, but it ultimately enhances processes as well. Operators can view commands and programming status alongside an image of their process, taken in real time, with no PC needed. This self-contained, intuitive, and sophisticated solution provides users with the ability to get an inspection up-and-running quickly and monitor and modify it easily — while still providing the advanced capabilities vision sensors offer.

Pick-to-light: error proofing

While the prior examples may prove advantageous for inspecting automated processes, error-proofing solutions also may be required for manual assembly processes, such as kitting operations for medical kits. These kits may contain multiple components for administering medication and performing medical procedures — making it imperative that each kit is complete and contains the correct components. To ensure kit assemblers select the proper items in the proper order, pick-to-light indicators and sensors can prove invaluable for operator guidance and pick verification. Indicator lights provide highly visible yet unobtrusive illumination, with sealed, easy-to-mount housings ideal for resisting dust and moisture in manufacturing environments. Sensors can be integrated into indicator lights to combine the function of visual guidance and verification feedback to the error-proofing monitoring system.

As an example, a pick-to-light indicator with integrated sensor may be placed above each bin containing kit components, with the sensing beam positioned at the entry point of each bin. As the job is initiated, the job light turns green, indicating the correct bin for the next pick selection. When the assembler reaches into the correct bin, the light beam interrupted by the assembler's hand initiates an output confirming the correct pick. The job light above the next pick location will then turn green, and the process effectively guides operators through assembly procedures. With this arrangement, a pick-to-light indicator with integrated sensor reduces assembly and picking errors while helping to speed component selection.

As demonstrated by the examples in this article, choosing the proper sensor to perform inspections leads to enhanced quality assurance and process control, as well as increased traceability. More importantly, it helps preserve the well-being of the patients to whom these products matter the most.

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