The role of digital components in photogrammetric instrumentations

Bibliographic data

Monograph

Persistent identifier:: 830281363

Title:: The role of digital components in photogrammetric instrumentations

Sub title:: symposium of Torino, Italy ; 2nd - 4th October 1974

Scope:: ca. 200 Seiten in getrennter Zählung

Year of publication:: 1974

Place of publication:: Torino, Italy

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 830281363

Illustration:: Illustrationen, Diagramme

Signature of the source:: T 15 B 1280

Language:: English

Additional Notes:: Literaturangaben

Other Title:: Nebentitel: Digital components in photogrammetric devices

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Corporations:: International Society for Photogrammetry, Commission, 2

Adapter:: International Society for Photogrammetry, Commission, 2

Founder of work:: International Society for Photogrammetry, Commission, 2

Other corporate:: International Society for Photogrammetry, Commission, 2

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2015

Document type:: Monograph

Collection:: Earth sciences

Chapter

Title:: TRENDS IN DESIGN OF DIGITAL EQUIPMENT FOR PHOTOGRAMMETRIC INSTRUMENTS. U. V. Helava

Document type:: Monograph

Structure type:: Chapter

9 Digital Servos Figure 5 shows a digitai servo system which is conceptually advanced in that the servo loop is closed inside a computer. The blocks shown in side the computer block are actually software functions. This design approach is of historical interest because it is not unlike the way the early analytical plotters handled the problem. The main difference is that the closing was implemented in terms of increments and with con siderable hardware involvement rather than a whole number fashion and in software as shown in the figure. In retrospect, the system is con ceptually advanced; at the time of those early designs that was the only way the job could be done. The servo closing ended up inside the com puter, because the computer and the interface were practically inseparable. Separation of the computer and the interface has been desirable for many years. Perhaps the strongest reason for this has been the phenomenal development rate of computers. A separate interface would allow, at least theoretically, replacement of one type of computer with a newer and better one. One system approach to achieve separation is shown in Figure 6. The computer still keeps track of the totals as far as the desired posi tion and the present position are concerned. The servo works in an incre mental environment, without any information within itself about the abso lute distances traveled, or still to be traveled. The computer "meters out" suitable command increments and the servo loop is closed on the basis of similar incremental feedback quantities originating from servo shaft encoders. Another approach for closing the servo loop in the interface, or within a special digital servo module, is shown in Figure 7. This is a fundamentally different approach, because here the computer has relin quished a significant part of its control. It simply sends to the servo the desired position and then trusts that the servo brings about the necessary motion to make the present position coincide with the desired one. Obviously, the servo logic must be reliable. In practice this is not an unreasonable objective; the servo logic need not meet reliability specifications any different from those set for a feedback data trans mission back to the computer. However, there is a less obvious require ment: in continuous real-time operation the servo response must be sufficiently good to avoid system problems. Such a response is not difficult to achieve when the system is designed for a human operator. His time constant is much longer than that of a well designed servo. In automatic systems, however, the servo is frequently a limiting factor. An extension of the design concept discussed above is shown in Fig ure 8. Here the logic of a digital servo is implemented by a micropro cessor. With increasing speed and memory capacity of microprocessor, this approach can be extended to include additional useful functions, such as acceleration, deceleration, and rate limiting as well as delayed action apd adaptive characteristics.

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