A new typewriter model has an inordinately heavy touch, much to the glee of the competition and the dismay of the engineers who designed it. Now, what’s the fix?
By Harshwardhan Gupta, Contributing Writer
My first job after graduating from IIT Bombay was with the Design Centre of a large Indian company, which among other things like refrigerators, padlocks and forklifts, manufactured manual office typewriters.
I joined the typewriter mechanism design group. A new model of the manual typewriter had been introduced about a year prior to my joining, and it was facing a lot of flak in the market for having an inordinately “heavy” touch. In other words, it was tiring out the typist very quickly, compared to the company’s previous models, and those from other competitors - who were rubbing their hands in glee!
Quite a few changes had been made over the previous model in one go, and the entire production, quality and design teams were at their wits’ end as to which of those changes had caused it. All sorts of theories were being bandied about by everyone, some bordering on fantasy, some blaming it on the new generation of young typists as being more delicate than the old warhorses. Our design team’s chief had already begun work on redesigning the 6-bar linkage of the typing keys to a more efficient 8-bar linkage system.
Having shown some spark as a design engineer, I was asked if I could bring some insight into the problem. The company had an internal standard for “good impression.” I then hunted around for a method or equipment to quantify the energy required to make that standard impression, but found none.
So I devised a simple rig - a guided 0.2 kg- weight falling from an adjustable height over a chosen key - and now I could measure and tabulate the potential energy required for creating a standard impression. Tests conducted with this simple device on various typewriters, including the old model, produced some startling data.
Our new machine consumed three times the energy of its nearest rival, which was the old model! Worse yet, all competitors’ machines were more efficient than ours. The crucial parameter was not the force but the energy required to type. Forces were comparable; energy consumed in our machine was much more. Here was the quantified proof! Now came the interesting part: The Whodunit.
Taking a cue from how IC engines are tested for their internal energy consumption, I started with removing the peripherals one by one: the ink ribbon feeder, the ribbon throw mechanism, the escapement to move the carriage… and repeated the impression test at each stage. I quickly found two culprits: The new ribbon advance consumed about 20% of the excess energy, and the new universal bar consumed the rest 80%! Here was the culprit!
The universal bar is a rod placed below and across all the key levers, so if any letter or the space-bar is pressed, this bar gets pressed down too. Its motion drives the ribbon advance, ribbon throw and carriage escapement. This bar is held up against the levers with a pair of springs.
In the older design, the key levers and the universal bar were pivoted on the same axis, so there was no relative motion between the two when a key was pressed. In the new design, the axis of the universal bar had been shifted some distance away, and the key pivot, the bar pivot and the contact point made up an almost equilateral triangle.
Each pressing of any key made the top of the bar rub along the bottom of the key, and this sliding motion under the normal force of the springs consumed the energy. The solution was obvious - move the pivot back to where it belonged. That and other improvements were made, always measuring the energy, and we soon matched the competitors’ energy values.
Contributing Writer Harshwardhan Gupta lives in Pune, India, has a B.Tech from IIT Bombay and runs his own machine design studio. He has designed many Word’s Firsts in various custom machines. Website www.neubauplan.com