A Suggested Improvement for the Computer-Aided Optical Melting-Point Device Michael Masterov Cooper Union for the Advancement of Science 8 Art, New York, NY 10003 Jude Sylvestre A. Philip Randolph Campus High School. New York, NY 10038
The melting-point device whose construction was recently reported in this Journal1 was further automated by the addition of sample holders and a mechanical arm. This addition will allow the device t o analyze several samples overnight without human supervision. The arm illustrated in the figure moves vertically and circumferentially, thus requiring two stepper motors. The arm hase, the melting point furnace, and the sample holders are rigidly fixed to a plywood platform. Thus no sensors are required, eliminating the most complex part of a robot. The sample holders, hase, and gears must he metal; the other parts of the arm can be plastic or Plexiglas (glued together). Set screws are glued to the capillary tubes, which are held hy the electromagnet. With 40:l gear reduction, positioning the arm to pick up the capillary presents no problems. However, proper insertion of the capillary into the 1.5 mm hole requires a funnel shape as the capillary tube can swing. Five-volt reed relays are used to switch stepper motor power. Output lines from the interface built for the melting point circuitry are used to drive t h e relays, so no other electronics are necessary. If access to a machine shop is availahle, and, if the components are ourchased on the survlus market, the device can be built for as little as $50. We gratefully acknowledge the helpful advice of John Bove of the Chemistry Department and the help of Kenneth Elter of the Chemical Engineering machine shop. .
' Masterov, M.: Plerre-Louis, 6.: Chuang, R. J. Chem. Educ. 1880, 67, A75-A77.
Me~hanicslam.All dimensions we In Inches. Only the distances between gear shafts are critical. A. Stepper motor brass gear. B. intermediate brass gear. C. Rotatingplatform brass gear. D. Plexiglas spacer cylinder. E. Rotating platform. F. Arm stepper motor. G. Bare stepper motor. H. Aluminum barn. I. Spool mounted on r t e p p r motw shalt. J. Fixed spwi acting as pulley. K. Monofllamentfishing line. L. Electromagnet. M. Set screw glued to capillary. N. 1.5-mm d i m capillary tubs. 0. Funnel to guide insertion. P. Furnace a capillary tube holder.
Volume 67
Number 11
November 1990
063
