Those who produce surgical instrumentation live with two constraints that are difficult to reconcile: high geometric variability of parts-scissors, forceps, retractors, needle holders, scalpel handles, retractors-and increasingly stringent regulatory requirements on content, location, and quality of marking. MDR 2017/745 and the UDI imposed by FDA and EUDAMED require permanent, legible, and correctly positioned DataMatrix codes; ISO/IEC 15415 (and its application reference AIM-DPM) defines minimum acceptable grading; ISO 17664 and AAMI ST79 require that the marking withstand repeated cycles of cleaning, citric/nitric passivation, and steam sterilization.
In this scenario, laser marking on stainless steel (typically 420, 440, 316L or 17-4PH) has emerged as the standard, often with picosecond fiber sources that produce annealing black marking that is impalpable and resistant to chemical cycling. There remains, however, a node upstream of the marking process: the placement of the layout on the part. And this is where the vision system and the software that handles it become crucial.
Because a simple preview is often not enough
Many industrial lasers are equipped with a field preview, made with a red pilot beam that projects the perimeter or contents of the layout onto the part. This is a useful feature for quick verification, but on surgical instrumentation it quickly shows its limitations.
The part changes often and rarely fits into rigid jigs; the areas useful for marking are small, curved, close to joints or reference holes; the content to be marked must adhere to coded positions (e.g., UDI code at a predetermined distance from the ring eye). With only the red preview, the operator sees where the marking will fall, but has no metrological reference against actual features of the part. On mixed batches this results in slow setups, first marking rejects, and the need for dedicated templates.
Side vision and TTL vision: two different approaches
There are two main architectures for integrating vision on a laser system. Side vision involves a camera outside the scanning head, positioned to the side with a field of view typically around 90×60 mm. It is robust, offers a wide field and lends itself well to automaticself-centering on pallets with many small parts. It is the most common choice in applications such as oil hydraulics or high-throughput automotive.
Instead, TTL (Through The Lens) vision integrates the camera inside the scan head, sharing the optical axis with the laser beam through a dichroic mirror. The field is smaller-about 20×16 mm with standard focal lengths-but it has a unique feature: what the camera sees is exactly what the laser will mark, on the same axis and through the same optics. By changing focal lengths, the field of view automatically scales with the marking field. There are no parallaxes, no geometric calibrations that have to be redone every time the lens is changed, and no shadow zones due to part geometry.
For surgical instrumentation, where marking insists on areas of a few millimeters and part variability is high, this coaxiality is the real discriminator. On a hemostatic clamp or scalpel handle, one does not care to see an entire pallet: one needs to see the marking area precisely, recognize a reference (an edge, a joint, a hole), and position the layout with respect to that.
The role of CadVision
On our FlyCAD software, vision is handled by the CadVision module, which translates the camera video stream into operational functions directly integrated into the marking environment.
The live preview feature shows the marking area overlaid on the layout in real time, allowing the operator to immediately assess alignment before launching the cycle.Auto-centering leverages pattern matching or blob analysis algorithms to automatically recognize part features (circles, contours, markers) and realign the layout accordingly, with typical tolerances on the order of a few hundredths of a millimeter. Manual centering is the function that, in surgical instrumentation, is most often used: the operator sees the part on the screen, drags the layout with the mouse or repositions it by pointing to two reference points on the image, and the software recalculates coordinates and rotation of the marker field.
The stitching function extends the field of view beyond the limits of the head’s optics. With the fixed head, the system captures multiple frames by moving the machine axes and recomposes them into a single wide image on which the operator can place the marking. It becomes essential when working on 150-300 mm long tools and wanting to place a code or logo at specific points on the part, without sacrificing the resolution of TTL vision.
A realistic application case
Consider a line for mixed marking of surgical scissors (length 14-18 cm, 420 steel) and needle holders (length 16 cm, 17-4PH passivated steel). The batches are small, from a few dozen to a few hundred pieces, with frequent reference changes. The required marking is a UDI DataMatrix of about 4×4 mm and 1.5 mm alphanumeric text, placed on the grip ring.
With a picosecond PowerMark system (UV or IR depending on finishing) equipped with TTL vision and CadVision, the operator loads the part into a generic V-shaped template, opens the marking file, and sees the ring framed by the head on the screen. He graphically drags the layout to center it on the available marking plane and confirms. Setup time per reference change is significantly reduced compared to a flow with dedicated templates, and the actual code position is visually verified before each first part. For longer tools, stitching allows you to see the entire useful portion and contextually position multiple contents (code, logo, batch text) without manually moving the part.
When it makes sense to choose TTL vision
TTL vision is not the universal answer. For high-volume production with medium-sized parts repeated on pallets, side vision remains more efficient. TTL becomes preferable when part variability is high, the marking area is small and well localized, and the operator must be able to visually intervene on positioning. These are exactly the conditions typical in surgical instrumentation, but also in other areas such as jewelry, precision small parts, and some aerospace machining.
Finally, it is worth mentioning that vision, however advanced, is an adjunct to the process. Final quality depends on the consistency between laser source, focal length, marking parameters and material: for surgical instruments, the typical combination is a picosecond source (1064 nm or 532/355 nm) with focal lengths from 100 to 254 mm, calibrated to specific stainless steels and validated on standard passivation and sterilization cycles.
