Machine Vision Lenses & Measurement Systems Manufacturer - POMEAS

Ask for the numbers that appear in the error budget and the cycle time: focus range in millimetres or dioptres at the working distance used; response and settling time with the actual driver; focus-position repeatability, and its drift with temperature; the effect of the focus setting on magnification; the aperture range and its effect on resolution; supply voltage, interface and whether the driver adds latency; operating temperature range; expected lifetime or cycle count; and the mechanical envelope and mass. Ask for the same list for both technologies, so the comparison is like for like rather than a feature list. [Data required: POMEAS product data]

Three architectures cover most cases. A motorized zoom lens with a focus group, where both zoom and focus positions are stored per recipe; this gives the widest coverage but adds two degrees of freedom to qualify. A fixed-focal lens with a motorized focus axis, which is simpler and more stable but cannot change the field of view. Or a fixed zoom with a focus-tunable element, where the field changes mechanically between product families and the fast focus handles the height variation within a family. Choose according to which requirement changes more often: if products differ mainly in height, keep the field fixed and vary focus; if they differ in size, the field has to change.

It has to be part of the specification, because mechanical and electrowetting systems age differently. A motorized system wears at its bearing, gear or screw and typically shows a slow loss of positioning repeatability; a liquid lens has no moving parts but its optical response can drift with temperature and with time, and its driving electronics matter as much as the lens itself. For a production station the useful figure is the focus-position repeatability measured after a realistic number of cycles, not a datasheet value measured on a new unit. If the supplier cannot provide a lifetime curve, plan an in-house endurance test on one unit and use the result to set the verification interval. [Test required]

Store as many as your product range needs, but verify each one the way it will run. A stored position is only valid while the mechanical zero, the temperature and the optical assembly remain unchanged, so the recipe needs a reference feature it can measure at each position and compare with the value recorded at qualification. Verify after the first article of a production run, after any long stop, and after any mechanical intervention. It is also worth recording, per position, the focus metric value that indicated a good image at qualification, because a comparison of that number over time is an early indicator of contamination, drift or a failing actuator.