I reached out to Dennis a while ago and received a reply! Well afterwards I sort of got distracted in following up or sharing this here
I would like to reach out again and hopefully bring to light some ancient documentation that might happen to be stashed away in an attic. Here is a reply I received from Dennis if anyone happens to be interested in this topic. Also if anyone has any questions for him feel free to share. As far as I know this keyboard is only know through a scant number of photos and very little documentation online.
Reply from Dennis:
First thank you very much for sharing the picture. I had long ago lost it. My family will get a kick out of it. Sorry for my late reply as I was traveling the past week.
Regarding the technology the keyboard was different from the Selectric but it did have a tactile " break away" feel to it. It was designed for the brokerage industry with a keyboard where each key represented a specific function like "Price", " Quantity", etc versus power typing but that said it did have a numeric keypad function, etc.
In 1974 the keys performed essentially the same function (as the brokerage industry) as part of the Terminals for the New York Stock Exchange Floor Trading System. At the time this was the first electronic floor trading system at the NYSE. These Terminals were installed in the "horseshoe" shaped trading posts where trading specialists gathered on the floor of the Exchange to conduct transactions. FYI I was the project manager at IBM responsible for this system. The controllers were located in a data center upstairs. I recall there were 16 such horseshoe shaped stations with 4 terminal each for a total of 64. I spent many nights on the floor working with many folks to get it working for the big switchover later that year. The trading posts don't bear any resemblance today .
The keyboard plastic material was a version of polypropylene and was a critical element of the actual key mechanism because its function depended on "living flex hinges" that demanded a functional plastic with long polymer chains such that when the living hinges were activated had very little internal friction. This was critical to prevent the living hinges from breaking with prolonged usage. FYI I was inventor of the key mechanism that was owned by IBM.
When a key was depressed it closed a contact as part of a cross XY matrix of printed circuit conductors called an elastic diaphragm switch also developed by IBM. The XY matrix was scanned to identify the key depression for processing.
If you like I can send you more info on the patent and maybe a photo of one of the mechanisms. They are at my home and would have to dig them out. Just let me know. I should note that the initial prototype key mechanisms were kind of crude and later were molded by a vendor for IBM and photo depicts this latter version. The story line about me testing them at home got picked up by one of the news media and was actually true. The project was on a tight schedule and I would heat and freeze them at home as as a sort of stress test as we were not sure at the time that the mechanisms would be durable enough. It was fun but scary at the same time since I was not sure if they would meet all the testing criteria of IBM testers.
Feel free to contact me if you need more or would like to discuss.
Thanks again and best regards.