Aligning flat optical surfaces to precise gap widths

The challenge

Several optical elements with a 20mm diameter are to be aligned on top of each other with a defined gap width and joined using UV-curing adhesives to form optical sub-assemblies. The following tolerances must be achieved:

  • Parallelism of the respective surface pairs better than 5µm/20mm
  • Concentricity better than 15µm
  • Defined air gap between 20µm and 25µm

The concept

To achieve parallelism in the joining partners over the entire surface, the optical element must be precisely handled and positioned with at least five degrees of freedom. Only the rotation around the surface normals is not absolutely necessary in this case.

At the same time, numerous macroscopic movements and interactions are required, for example when applying adhesive, feeding and removing the components and measuring the gripped components.

Building blocks

Microassembly platform

By implementing the process on a SmarAct Automation P50 microassembly platform, the two orders of magnitude of positioning, metrology, adhesive supply and component supply can be seamlessly combined. The Cartesian motion system of the P50 accomplishes the macroscopic movements with high dynamics and repeatability of up to 2 µm.

Component handling

A handling module with a top-mounted camera installed on it can be used to reliably move and pre-position the components. An equally installed dispenser module enables the precise application of the optical adhesive in the necessary quantity and position, which were determined in the preliminary study. Gripped objects are measured using a bottom-mounted camera fixed in the workspace.

Active aligment

The active alignment of the optics, on the other hand, is carried out by a SMARPOD positioning system. This hexapod-like 6D kinematics enables all necessary movements with repeatability of typically 100 nm or better. Cameras attached to the workpiece clamping enable continuous measurement of parallelism and the adhesive gap.

Supply and removal

The components are supplied via an automatic magazine feeder attached to the side of the system and are also removed from there after alignment. The scope of the magazine system is designed depending on the required autonomy and cycle time.

Application software

All aspects of the process can be operated and adjusted via the system's application software. Various separate operating modes are available, e.g. for user operation, developer operation and administration. Thanks to the modular script system, adjustments to the process flow can be implemented at any time.

Process-specific developments

Every process is different. Further modules and devices required for your specific process are identified during the concept phase. Solutions from a growing portfolio of flexible standard modules are combined with process-specific special solutions.

The alignment and assembly process

Loading the components

The first element is removed from the input magazine, measured on both sides and fixed in the clamping fixture.

Adhesive dispensing

The previously determined amount of adhesive is applied to the edge area of the glass surface in a defined pattern.

Precise pre-alignment

The second element is gripped, measured on both sides and positioned above the first element at double the nominal distance.

Active alignment in position, tip and tilt

The lower element is aligned using a SMARPOD. The position is controlled to the three gap widths, which are detected by the tangential measuring cameras.

Adhesive curing by UV

The adhesive is activated by UV light so that the components are firmly bonded.

Inspection and removal

After adhesive curring the assembly is illuminated and examined to verify that the gap width and the respective positions of the components conforms to the defined tolerances. The inspected end product is then removed from the assembly mount and placed into the output magazine.

Achieve unparalleled precision in parallel alignment of components

SmarAct’s solutions enable fully automated assembly with alignments at micrometer-level accuracy, as demonstrated in our application example. If your project demands similar capabilities or tailored solutions, our sales engineers are ready to assist you — contact us today!

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