Integraph with transfer of direction by a linkage parallelogram, system Abdank-Abakanowicz/Coradi (large model)
As already mentioned several times, the problem of transferring a direction, extracted from a given curve, to a knife-edged wheel was one of the central questions that Bruno Abdank-Abakanowicz (1852-1900) had to solve in his quest for a reliable and accurate integraph. He had been investigating this problem already in Poland in the end of the 1870s. After moving to Paris, new ideas came out of his cooperation with David Napoli (1840-1890); ideas, which even resulted in the commercial production of an integraph by the Barbier workshop in Paris (see CNAM 44165-0001-). But it took the experience and insight of Gottlieb Coradi (1847-1929) to find a feasible solution that enabled the construction of a really successful and lasting commercial product. Abdank-Abakanowicz gratefully observed: "Mr. Coradi in Zurich, the renowned maker of precision instruments, has dealt with the construction of our integraphs; these are now manufactured by him in a correct way. Mr. Coradi has kept from the earlier integraphs only the basic principle; the mechanical realisation of that principle and the transfer of the movement of the directrix to the wheel, which is extraordinarily solved, are solely his merit." ("Herr Coradi in Zürich, der bekannte Erbauer von Präzisionsinstrumenten, hat sich mit der Konstruktion unserer Integraphen beschäftigt; dieselben werden jetzt von ihm in korrekter Weise ausgeführt. Herr Coradi hat von den früher konstruirten Instrumenten nur das Grundprinzip behalten; die mechanische Verwirklichung dieses Prinzips und die Uebertragung der Bewegung vom Richtlineal auf die Rolle, die in musterhafter Weise durchgeführt wurde, sind ausschließlich ihm zu verdanken": Abdank-Abakanowicz 1889, 59).
Coradi founded his workshop 1880 in Zurich, after having cooperated with his brother in law Albert Ott in Kempten from 1874 until 1880 (under the name Ott & Coradi). Albert Ott and Gottlieb Coradi had met during their apprenticeship at Starke & Kammerer in Vienna and had also come to know of the planimeters produced at Starke & Kammerer (orthogonal planimeters of the Wetli-Starke type, but also polar planimeters of the Miller-Starke type). In Zurich, Coradi at first dealt almost exclusively with the production of planimeters. A special field was the introduction of so-called precision planimeters, which tried to combine the advantages of the orthogonal and the polar planimeter, respectively. This experience made Gottlieb Coradi an ideal counterpart for Abdank-Abakanowicz und Napoli; as one will see, his solution to the problem was brilliant.
Coradi integraph, system Abdank-Abakanowicz = fig. 62 from Abdank-Abakanowicz 1889, 65
What he did was the perfection of an idea which already had been investigated by Abdank-Abakanowicz and Napoli, at least partially: the use of a linkage mechanism - more precisely: a linkage parallelogram - which can easily be identified on the picture above. Generally, a linkage parallelogram is the simplest mechanism to keep two directions parallel to each other, as it is the characteristic property of a parallelogram to keep the pairs of sides without common joints parallel. It was "only" left to pay attention to the fact that changing the form of the linkage parallelogram automatically changes the distance between parallel sides, which seems inconvenient. But as in an integraph the distance between tracer pin and knife-edged wheel also varies, these two "distance problems" could be melted into one - which in addition was not new. Coradi solved the problem by executing all gliding joints as carriages led by tracks, thus also minimising at the same time the friction between the different parts of the instrument. In this way, the instrument did not only work smoothly and correctly, but was also controlled by the movement of the tracer pin along the curve to be integrated.
Coradi integraph, large model, instrument no. 51 (CNAM), full view
Coradi integraph, large model, instrument no. 51 (CNAM)
Comparing the drawings of the 1889 German edition of Abdank-Abakanowicz's book (the French edition of 1886 does not yet mention any cooperation with Coradi) and the photographs of the Conservatoire's integraph (serial no. 51, made c1901), one can see that during more than a decade almost nothing in the execution of the instrument has changed or had to be changed - another proof of the high and extraordinary quality of Coradi's construction.
Coradi integraph, large model, instrument no. 51 (CNAM), detail
It was only around 1903 that a new model eventually replaced this first type of a commercially and successfully produced integraph.