Having worked as a EE in the ...dim mists of time..., I saw the introduction of the micro computer and the Programmable Controller (now called the PLC but then called the 'PC' -- damn IBM and their theft of the acronym).  The 'PC' was in response to a General Motors specification that both Modicon and DEC tackled.  (And the rest ...as they say... is history.)

Now also being a railway enthusiast and an amature technology historian, I was aware that in 1843 on the English railways, an 'interlocking machine' was developed for the use at Bricklayer's Arms Jct. to control the switches (points to the non-Americans amongst us) and signals.  This was later developed into several versions--all based on patterns of deliberate mechanical interferences that prevented the movement of certain operating levers.  This prevented conflicting routes being set up at a railway junction and/or forcing particular sequences of lever movements.  (There is an excellant tutorial on this at http://www.du.edu/~etuttle/rail/lock.htm.)  At any rate the components for these machines became standardized and could be individually 'programmed' for any junction.  The 'computing bed' (of dogs and locking bars), then, could be said to be a true 'programmable' mechanical logic device.

The railway interlocking machine would have been my hands down candidate for the first industrial mechanical programmable controller ...if it weren't for Joseph Marie Jacquard and his card programmed loom around the turn of the 19th century (see http://history.acusd.edu/gen/recording/jacquard1.html).  (I find it interesting that this system represents 1/2 of an almost Turing Machine.)

So, let me throw it out there.  Do any of you have any candidates that would predate the two items above?  With that in mind, let me set some criteria:

1.) It has to be a mechnical device

2.) It has to be programmable, i.e., relatively easy changes in the components would be all that would be required to change the system's logic

3.)  It should be for an industrial purpose, i.e., used for the production of goods and services -- not an entertainment automiton, an astronomical display device, or a time piece

4.)  I would also have to eliminate assembly and production jigs and fixtures (serving a different purpose) or valve gear (too simple a mission).

Frank A. Jur, P.E.
Electrical Engineer