08-05-2012, 05:04 PM
A PHOTOELECTRIC DECIMAL-CODED SHAFT DIGITIZER
A_Photoelectric_Decimal-Coded_Shaft_Digitizer-dnb.pdf (Size: 1.41 MB / Downloads: 34)
PRINCIPLES OF OPERATION
coded shaft digitizer. Phototubes are used to read the posiof
masks, permitting static as well as dynamic readout with
minimum loading of the measured shaft. Reading is done with The Photoelectric Decimal- Coded Shaft Digitizer
several units, each reading a digit of the decimal number consists, in essence, of several similar reading units,
representing the shaft position. A special decimal code each unit reading one of the digits of the decimal numenmploying
5 phototubes per decade is used to avoid intra- ber equivalent to the shaft position. Thus the first unit
decade ambiguities. Inter-decade ambiguities are prevented reads, say, tenths of revolutions; the second unit,
by using two masks on all but the first decade. An experimental
digitizer, using standard components, is described. geared 1 to 10, reads revolutions, and so on. We shall
describe the operation of the first two of these units,
the units decade and the tens decade. All higher decades
operate in a manner similar to the tens decade.
INTRODUCTION
1 shows the configuration of the first decade.
Five photocells with defining slits are equally spaced
In recent years there has been increasing need for 360 apart on an arc. A simple 1800 mask is attached to
shaft digitizers in the field of measuring, control, and the shaft so that it may rotate between the photocells
computing mechanisms. The requirements for these and a lamp. As the shaft rotates, and if the lamp is
digitizers vary considerably in range, resolution, load- flashed at appropriate times, the 5 phototubes will be
ing, shaft speed at readout, readout rate, and numbering illuminated in succession and obscured in succession.
system. This article describes a new shaft digitizer de- One, and only one, phototube will changeits conductance
veloped to meet the following requirements: state every 360. An unambiguous (synoptic) decimal
code, as shown in Fig. 2, may be formed from these
1. Resolution: 1/100 revolution changes. The second decade has its rotor geared 1 to
2. Range: lOn -1, where n is any desired integer 10 to the input shaft.