Tokyo-Researchers at the Mechanical Engineering Laboratory of Japan's Ministry of Economy, Trade and Industry (the former Ministry of International Trade and Industry) and Olympus Optical Co. have developed what they believe to be the world's smallest numerically controlled lathe, which they expect to speed the development of micro-machines.

The group had previously developed a micro-lathe, with a slide driven by piezoelectric actuators. But it only had axis control that limited the accuracy and complexity of the machined parts. The group decided to add numerical control to give it the functionality of standard machine tools.

Measuring 32 mm long, 25 mm wide, and 30.5 mm high, the lathe weighs just 100 grams. The spindle drive is a coreless 1.2W dc motor that produces a maximum 15,000 rpm. Modified inchworm type micro-slides are used, with the slides guided and held by friction with a positioning accuracy of 25 nm. The slide of the micro-lathe can be smoothly fed at up to 0.4 mm per second.

A new micro-linear encoder, developed by Olympus Optical Co., detects movement of the slide. Light from a surface-emitting laser is reflected from a scale on the slide and then read by a detector. Olympus bills it as the smallest encoder of its type, measuring just 4.5 x 5.5 x 2.1 mm and weighing only 0.4 grams. It can detect positioning to an accuracy of 62.5 nm. Programmed instructions and feedback from the encoder are analyzed at 5 millisecond intervals to control the piezoelectric actuators. The numerical controller is a purpose-built single board controller.

In test runs, the tiny lathe has produced a brass needle 0.05 mm wide and 0.6 mm long and screws that are only 0.05 mm thick. Despite the promise of machining such tiny precision parts, the tiny lathe is still a laboratory curiosity. "The cost of making one NC micro-lathe is still so high that this is far from being ready for practical use," says Fumitake Chisaka, a researcher involved in developing the lathe. He adds that it would be possible for them to bring one of the lathes to other laboratories to custom-make objects on a negotiated basis.

For more information about the micro-lathe from the Mechanical Engineering Laboratory of Japan's Ministry of Economy, Trade and Industry:Enter 565