SE439132B - PRINT QUALITY CONTROL SET AND DEVICE - Google Patents

Description

The invention is described in more detail in connection with the accompanying drawing, in which Fig. 1 schematically shows the parts of a dot matrix printer which are of interest in connection with the invention, and Fig. 2 shows included electrical circuits.

PREFERRED EMBODIMENT FIG. 1 schematically shows a writing paper 1 with characters printed by means of a printhead type printhead 2. In the left margin of the writing paper, the print head has also printed a dot pattern 3 for each print line. The pattern is designed as a dotted line perpendicular to the direction of movement of the print head and has been achieved by all the writing elements of the print head. An optical sensing means 4 is arranged in such a way that when the row alternates, the dot pattern 3 passes under the sensing means 4.

Fig. 2 shows in more detail a device according to the present invention. The optical sensing means 4 comprises an LED 7, which illuminates the writing paper under a photodiode line 8 with shift registers of, for example, make EGB. 3 direction of movement. With the aid of the shift register, each diode is read in turn at a speed determined by a control means 12 included in a computer 6. In this case, the clock frequency of the control means has been selected to 50 KHz and a sampling frequency to 300 Hz, giving a sweep time of 2.56 ms and about 12 sweeps per point in the dot pattern 3. The signal from each photodiode is transmitted to a comparator 5 where it is amplified in a direct voltage amplifier F and compared with the voltage from a reference voltage source R in a differential amplifier D.

Signals with a higher amplitude than the reference voltage are assigned a one in the differential amplifier, while signals with a lower amplitude are assigned a zero. The digitized signals are read by the computer 6, where a counter 9 adds all ones according to given conditions. A condition may, for example, be that at least four consecutive ones are required for the counter to add these. After three readings of all diodes without the above-mentioned conditions being met, the counter is read, after which it is reset. A condition for a point to be registered at the passage of the dot pattern 3 past the sensing means is that the counter 9 adds 8305478-3, for example 40 ones. In a register 11, the number of registered points is compared with the number of write elements of the printhead 2. In the event of a deviation between these numbers, a signal circuit 11 is affected, which emits an alarm signal.

Claims (5)

8305478-3 1D PATENT CLAIMS A method of using a photosensitive circuit to check the print quality of printers, preferably dot matrix or inkjet printers, characterized in that the printer writes a predetermined symbol in relation to a predefined area, the symbol being read in connection with line rotation with by means of the photosensitive circuit, the signal pattern from the photosensitive circuit is compared with a signal pattern corresponding to a correct representation of the written symbol, and in the event of a deviation between the two signal patterns an error signal is generated. Device for controlling the print quality of preferably matrix or liquid jet printers according to claim 1 by means of a photosensitive sensing means (UL), characterized in that the photosensitive sensing means of the device is arranged such that in connection with line rotation one of the printers in relation to a written specific area written, predetermined symbol passes under the sensing means, generating electrical signals, the amplitude of which depends on the color contrast of the symbol against the writing medium, and circuits for comparing these signals with a predetermined signal pattern, wherein depending on deviation between the the sensing means generated and the predetermined signal pattern a signal is emitted. Device according to claim 2, characterized in that the written symbol forms a dotted line extending simultaneously in the paper feed direction of all writing elements at the same time. Device according to claim 2, characterized in that the written symbol for every second line originates from writing elements with odd serial numbers and for every other line from writing elements with even serial numbers. 5. Device according to claim 2, characterized in that the signal emitted due to deviation between the two signal patterns controls an alarm circuit.