Stretcher

by Adrian Glasser

This is a blog about a computer controlled stretching instrument to be used in laboratory research for stretching soft and maleable lenses.

This stretcher has eight 'arms' that can be attached to a sample to allow the sample to be stretched radially. Each arm is attached to a linear translation stepper motor. The mechanical parts of the stretcher were designed in CAD software to be 3D printed on a high-resolution 3D printer. The stepper motors are chosen for their size and linear range of travel suited to the particular stretching application and the 3D printed parts are designed and printed from materials of sufficient strength to withstand the forces required for the particular stretching application.

CAD image of the stretcher design.
CAD diagram of stretcher

The stretcher 'platform' sits on top of an octagonal acrylic chamber. The chamber is transparent to allow for optical measurements of the lens during stretching. The chamber can be filled with water or saline to allow the stretching to be performed in a liquid environment. The platform of the chamber is designed so that a thermometer and a water heater can be placed in the octagonal acrylic chamber to allow the saline to be maintained at a set temperature.

The software in the video below is being run on a laptop computer. The software communicates with a USB microcontroller and an electronic circuit (seen in the background of the video below). The software sends instructions to the microcontroller which in turn sends commands to stepper-motor driver boards to control the speed and movement of each stepper motor. These stepper-motors have a resolution of about 1.5 microns. The software application is simple demonstration software for rudimentary control of the stretcher and live video capture from the USB camera viewing the stretcher. The software allows for the motors to be run forward, backward or in cycles for a user-specified distance.

The video is best viewed by clicking on the full-screen icon at lower right on the video.