Tele-operated micro assembly of nano actuators
The precision during an assembly is a crucial impact factor for the achievable precision of a miniaturized sensor or actuator. Smaller deviations in the positioning of the components of an assembly result in better overall performance, accuracy class – and higher sales price. Miniaturized products, which are designed to work with micro- or nanoscale resolution should be assembled with at least one, better two, orders of magnitude better resolution. How to assemble irregular shaped or difficult to grip objects with such an accuracy? Such precise manual assembly is only available after long years of training and cannot be expected a full working day.
A system to support you in your assembly task is very helpful if micro assembly is new to you, if there is no knowledge available or you do not need to assemble too often with these high requirements. Assembling actuators, which allow for nanometer precision is used as an example here. Piezo-driven actuators are around for quite some time when it comes to high precision positioning. From the various possible designs, we chose the rotating-ball-type actuator. A steel ball is rotated with this piezoelectric actuator. Three of these allow the actuator to either run on arbitrary surfaces or to move a cover plate.
On one actuator ceramics three single ruby hemispheres are glued on laser-structured electrodes. The electrodes outer diameter is 1 mm, as is the ruby hemisphere’s outer diameter. Glue is dispensed on every electrode. Care has to be taken to use just the right amount of glue, so that it is not flowing between the electrode structures when the hemispheres are placed to avoid malfunction of the assembled nano actuator. This assembly was so far performed manually under a light microscope. Dispensing the glue and placing the rubies are the critical process steps.
The video shows how the assembly is performed in a tele-operated manner on our MiCROW-Pro. The videos are original footage from, as it is presented to the operator in our MiCROW Control Application. A 12x microscopy zoom optics records the overview scene, which is presented in the center of the video. Each tool is observed from the rear with a dedicated tool camera, showing the vacuum gripper to the left and the dispensing tool to the right.
A time-pressure dispenser is used to dispense the glue from a standard 3 cc cartridge through a capillary with an inner diameter of 0.21 mm. The pressure pulse is triggered by a button press on the gamepad, which is our standard input device. It is possible to trim the pressure pulse to the millisecond in a range from 10 to 100 ms. With the dispenser tip slightly tilted the dispensing position can easily be tracked and defined in the main camera image.
After wetting all electrodes, the ruby hemispheres are picked up with the vacuum gripper and placed on the glue and pressed down to the electrodes. In this process step the redundant glue is pressed out and the film between electrode a ruby is equalized. With the hardened glue and the accurate positioning the actuator is able to perform movements with nanometer precision.
The critical assembly steps could be improved for the operator as the assembly could be paused anytime. Movement speed of the manipulator can be varied and improves the workflow as well as the positioning accuracy. That is because with lower movement speeds the tele-operated manipulator can be positioned more precisely. Additionally, the assembly can be documented by images and recorded for reference.