Importance

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Abstract

The invention relates to a scanner for clock discs driven by d.c. motors and provided with light transmitting slits for putting out signals to an evaluation circuit in typewriters or office machines of similar construction, with the slits (4) being scannable by a dual light barrier arrangement (5) in the form of a position sensor and including a light source (6) and two light receivers (7, 8). In order to ensure accurate control of the d.c. motor (1) and of the driven members connected therewith, e.g. a print wheel or a printer carriage, it is necessary that the signals at the two output channels, which are offset by one-quarter of a clock pulse period, do not go above or below a certain maximum value. Electrical control devices for such a necessary adjustment process are already known but they are less suitable for inexpensive office machines. The adjustment of the two sinusoidally configured signals at the output channels of the light receivers (7, 8) is realized according to the invention in that the cross section of the bundle of light beams coming from the light source (6) can be varied in the simplest manner by means of adjustable shutters (21, 22) which can be manually pivoted into their beam path. This permits rapid adjustment of the maximum values of the output voltages in the light receivers (7, 8) to a predetermined voltage.

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First Claim