Electrokinetica The Electro-mechanical Museum

Numerical Control - the efficient way to manufacture

Automated manufacture has been in use for over two centuries. One of the first machines to be programmed by punching holes in a storage medium was the Jacquard loom, invented in 1801. This enabled a complex woven pattern to be created by following a program stored on a string of punched cards. By the 1970s many branches of industry were using machines controlled by standard punched tape, that was in widespread use for teleprinters and computers generally.

Dyna-Turn CNC Lathe...

Dyna-Turn at work

This centre lathe is not quite an EK artefact yet because it still has a job to do. It lives in the workshop that makes our spare parts and Lucien helps look after it, so it will be heading up to EK once it officially retires. The Yamazaki Dyna-Turn 2L uses a Fanuc 5T numerical control system that was state-of-the-art when it was built in 1979. Its core is a custom microcomputer based on the 8080 CPU, enabling the machine to generate a tool path from a program entered in ‘G-Code’, a human-readable CNC language. It can be programmed online from its control panel, via serial from a teleprinter, or by loading a tape into its internal optical reader. The controller operates the lathe by means of electronic variable-speed drives for the axis motors and spindle, plus many electro-hydraulic valves that control actuator rams and motors powered by a central hydraulic power pack. It monitors the position and speed of the axes using tachogenerators and encoders, capable of resolving the tool position in increments of 10 micrometres. These provide the feedback for a tight servo-system that ensures the tool follows the path defined by the program as quickly as possible within the necessary tolerance.

...Still at work

This machine is now over 30 years old, yet it is still busy on a daily basis manufacturing precision components for industry, turning out accurate results all day long, and hasn’t had a single breakdown for over a quarter of a century. With consumer technology now so short-lived and expendable it is reassuring to know that a computerised machine can have a useful life measured in decades, with only standard consumable parts such as carbon brushes, seals and bearings needing periodic replacement.

Tape reader

Tape reader

Finished part with its tape

Finished part with its tape

Ingesting a program tape

Ingesting a program tape

Inside the machine

By comparison to a recent machine, there is a lot of hardware inside the control cabinet. Large numbers of ICs and discrete components are used in the controller, for functions that would today be implemented in software or using larger scale integration in hardware. The machine’s firmware, for example, is stored in 28 EPROM ICs. The electrical equipment is divided into two cabinets, one for the controller itself and another for the variable-speed drives, relays and transformers. A further cabinet holds the hydraulic gear. Modern variable-speed drive technology favours inverter-controlled AC motors for their low maintenance and high efficiency. When this machine was built, such drives were in their infancy and the standard choice for industrial work was the DC commutator motor, supplied from 3-phase AC through a controlled rectifier bridge. The Dyna-Turn spindle is driven by a 7 hp 4-pole DC brush motor, whilst the axis motors are permanent magnet DC types. Each carries on its shaft a tachogenerator, essentially a small but very precise and stable DC generator, which sends to the controller a feedback voltage directly proportional to the motor velocity. The machine’s fixed-speed motors, such those for the hydraulics and various lubricating and cooling pumps, are ordinary 3-phase AC induction machines.

Fanuc 5T control

Fanuc 5T control

Electrical cabinet

Electrical cabinet

CPU board

CPU board

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