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Browse Prior Art Database

Improved Value Control Dial Mechanism

IP.com Disclosure Number: IPCOM000100219D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 3 page(s) / 67K

Publishing Venue

IBM

Related People

McManigal, DF: AUTHOR

Abstract

Computer workstations, such as the IBM 5080 Display System, use potentiometers as mechanisms for input of continuously-variable values. Potentiometers are relatively expensive and bulky, and they are limited by mechanical stops or a "dead zone" which must be compensated for by computer programming or other means.

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Improved Value Control Dial Mechanism

       Computer workstations, such as the IBM 5080 Display
System, use potentiometers as mechanisms for input of
continuously-variable values.  Potentiometers are relatively
expensive and bulky, and they are limited by mechanical stops or a
"dead zone" which must be compensated for by computer programming or
other means.

      This device provides a low-cost, low-mass mechanism for
translating shaft position into a digital value.  The mechanism
(Figs. 1 and 2) generates a stream of voltage pulses which are
positive-going for one direction of travel, and negative-going for
the other direction. Conventional electronic circuitry can then be
used to translate these pulses into digital signals suitable for
control of an up/down counter, such as the industry standard part
SN74193, which can be cascaded to achieve any desired resolution.

      The functional elements of the invention are a light source, a
slot mask, a rotating disk with a distinctive opaque edge pattern,
and a photocell which drives an appropriately designed differentiator
circuit.  The slot mask must be aligned precisely with the vertical
(radial) edges of the edge pattern, but other mechanical adjustments
are not critical.

      Rotating the disk produces the voltage waveforms shown in Fig.
4.  The light source, slot mask, and differentiator must be designed
for a particular range of speeds, and excessively slow rotation of
the disk will fail to produ...