For manufacturers working with films, foils, thin glass, and sensitive materials, measurement accuracy is more than a quality metric — it’s a competitive advantage. Here’s how confocal differential systems deliver it.
In high-precision manufacturing, the difference between a passing part and a rejected one can be less than a micron. Traditional contact-based measurement methods — calipers, micrometer probes, mechanical gauges — introduce their own variables: tool wear, surface deformation, operator variation, and an inability to handle delicate or ultra-thin materials without risk of damage.
Confocal differential thickness measurement eliminates these variables entirely. By deploying two opposing non-contact sensors simultaneously, this technology measures material thickness with sub-micron accuracy — in real time, without touching the part.
What is confocal measurement?
Confocal sensors use a focused beam of light that only returns a sharp signal from objects at a precise focal distance. By scanning focal depth, the sensor determines exact surface position. Two opposing sensors working in tandem — one above, one below the material — calculate thickness from the distance between the two surface readings, independent of any variation in the material’s Z-position.
How dual confocal differential measurement works
The “differential” in confocal differential measurement is the key insight. Rather than measuring absolute position or relying on a fixed reference surface, the system continuously subtracts the readings of two aligned sensors facing each other across the measurement gap.
High-power diode lasers, with a wavelength of ~808 nm, are particularly effective due to their near-visible light properties, which maximize absorption. Fiber lasers, which are often integrated into more complex motion systems, operate at 1064 nm. Fiber lasers have an added advantage in that they are easily integrated into automated systems and can be adjusted for various PCB designs. This flexibility makes them ideal for manufacturers looking to optimize production lines and quickly adapt to changing market demands’ can be adapted to your specific application.
Step 1 Sensor Alignment
Two Keyence CL-series confocal sensors are mounted coaxially above and below the material path, separated by a precisely known gap distance.
Step 2 Simultaneous surface acquisition
Both sensors detect each surface simultaneously, measuring the distance to the top and bottom surfaces of the material at the same X-Y coordinate.
Step 3 Differential calculation
Thickness = (known gap) − (top reading) − (bottom reading). Z-axis vibration or drift affects both sensors equally and cancels out.
This differential approach is what makes the technology so powerful for real-world manufacturing environments. Because both sensors are affected equally by any mechanical vibration, thermal drift, or ambient disturbance, these error sources cancel out in the subtraction. What remains is a pure thickness signal — accurate to ±1 µm in properly configured systems.
Contact / Single-Sensor Methods VS Confocal Differential Thickness |
| Risk of surface damage on delicate materials | Fully non-contact — zero risk to surface |
| Probe wear introduces drift over time | No wear; consistent accuracy over time |
| Cannot measure in-motion or in-process | Supports scanning, roll-to-roll, static modes |
| Z-axis variation corrupts readings | Z-drift cancels in differential calculation |
| Slow — requires manual repositioning | Rapid multi-point scanning in one pass |
| Operator-dependent repeatability | Automated, repeatable to ±1 µm |
The ROI case for precision measurement
It’s tempting to treat metrology as overhead — a cost center that adds time and equipment to a production line. The financial reality is the opposite. Investing in precision thickness measurement systems delivers returns across three distinct vectors: scrap reduction, regulatory compliance, and process intelligence.
↓ Scrap |
±1 µm |
Real-time |
| Catch out-of-tolerance parts before they become finished goods — or customer returns | Accuracy that enables tighter process windows and higher-specification product offerings | Inline data feeds process control systems, enabling immediate corrective action |
For manufacturers in electronics and medical devices, where material thickness directly affects electrical properties or device performance, the stakes are especially high. A film that is 2 µm too thick in a capacitor stack changes its capacitance. A filter membrane outside its thickness specification changes its flow characteristics. These aren’t cosmetic defects — they’re functional failures that contact-based or manual inspection methods may miss entirely.
Process control advantage
Bold’s 3DS1430 system’s closed-loop architecture feeds real-time measurement data directly into production monitoring. Rather than sampling finished goods after the fact, operators can observe thickness drift as it develops — and correct upstream process parameters before any material goes out of spec. This shifts quality assurance from reactive to preventive, which is where the largest cost savings accumulate.
There’s also a total cost of ownership advantage: confocal sensors have no moving contact parts that wear or require calibration offsets over time. A mechanical probe station needs regular tip replacement and recalibration. A confocal system’s accuracy is inherent to its optical design — it doesn’t degrade with use.
Finally, for manufacturers targeting premium or regulated markets — aerospace components, implantable medical devices, advanced filter media — the ability to provide full measurement traceability for every part, at every scan position, is increasingly a customer requirement, and no longer a differentiator. Systems like the Bold CDM1820S and 3DS1430 are designed from the ground up to support this kind of documentation-grade data output for compliance.
Which system is right for your process?
The right platform depends on whether your production flow is static or in-motion, your required measurement width, environmental constraints (cleanroom vs. industrial floor), and throughput demands. Bold Laser Automation’s engineering team works directly with manufacturers to match system configurations to process requirements — including integration with existing automation lines and custom fixturing for non-standard material geometries.
Talk to a Bold metrology specialist
To learn how confocal differential measurement can be integrated into your production environment, fill out our Contact Form or call us today. We love hearing from you!
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