JPH012014A - Synchronous signal detection device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a synchronization signal detection device used in laser beam printers and the like.

(Prior art) As shown in FIG. 4, a synchronization signal detection device generally detects a laser beam emitted from a laser l and deflected by a rotating polygon mirror 2 with a light receiving element 4 via a mirror 3. The output signal of the light receiving element 4 is waveform-shaped by a waveform shaping circuit 5 to obtain a synchronization signal.

Further, in this synchronization signal detection device, as shown in FIG. 7, the output signal of the light receiving element 4 is differentiated by a differentiating circuit to obtain a synchronization signal at the zero cross point.

(Problems to be Solved by the Invention) In the former synchronizing signal detection device, when the intensity of the laser beam incident on the light receiving element 4 changes, the output signal A of the light receiving element 4, as shown in FIG. B is waveform shaping circuit 5
When the waveform is shaped at the threshold level, six timing deviations occur in the synchronization signal. In this case, the intensity of the laser beam incident on the light-receiving element 4 changes due to the difference in the reflectance of each surface of the rotating polygon mirror 2, and due to the difference in the reflectance of the laser beam LB.
The cause is that due to the surface inclination of the rotating polygon mirror 2, the light is moved on the light receiving element 4 from the normal position 1i7LBo to LBI and LB2 as shown in FIG. Furthermore, in the latter case, differentiation is performed, which deteriorates the signal-to-noise ratio, which also causes a timing shift in the synchronization signal.

(Means for Solving the Problems) The present invention provides two light-receiving elements having a dividing line in a direction perpendicular to the traveling direction of the light beam in the travel path of the traveling light beam, and The difference between the outputs of the light-receiving elements is calculated, and a synchronization signal is extracted from the zero-crossing point of the calculated output.

(Example) 1 and 3 show one embodiment of the invention.

In this embodiment, for example, in a laser beam printer, a laser beam emitted from a laser 11 and scanned by being deflected by a rotating polygon mirror 12 is detected by a light receiving element 14 via a mirror 13. It consists of two light receiving elements 14a and 14b having a dividing line in the direction perpendicular to the scanning direction, and sequentially detects the laser beam.The output signals of the light receiving elements 14a and 14b are transmitted through amplifiers 15a and 15b. A subtraction circuit 16 calculates the difference. As shown in FIG.
5b's output signal appears with a time lag, and the synchronization signal can be extracted from the zero-crossing point of the output signal O of the subtraction circuit 16. The position of this zero cross point is the light receiving element 1.
Even if the intensity of the laser beam incident on 4a and 14b changes, it does not shift, and a stable synchronization signal can be obtained.

Note that the present invention can also be applied to detecting a traveling light beam or positionally centering the light beam in a device other than a laser beam printer.

(Effects of the Invention) As described above, according to the present invention, two light receiving elements having a dividing line in a direction perpendicular to the traveling direction of the light beam are disposed in the travel path of the traveling light beam, and The difference between the outputs of the two light-receiving elements is calculated, and the synchronization signal is extracted from the zero-crossing point of this calculated output, so even if the intensity of the light incident on the light-receiving element changes, the zero-crossing point will not change in terms of timing. First, there is no possibility of timing deviation of the synchronization signal. Furthermore, there is no deterioration of the signal-to-noise ratio due to differentiation, and stable detection of synchronization signals is possible.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a light incidence part in an embodiment of the present invention;
Fig. 2 is a block diagram of the same embodiment, Fig. 3 is a timing chart of the same embodiment, Fig. 4 is a diagram showing a conventional device, and Figs. 5 to 7 are diagrams for explaining the conventional device. It is. 14a, 14b... Light receiving element, 16... Subtraction circuit. 34 Figure

Claims (1)

[Claims] Two light-receiving elements having a dividing line in a direction perpendicular to the traveling direction of the light beam are arranged in the travel path of the traveling light beam, and the difference between the outputs of the two light-receiving elements is calculated, and the calculated output is A synchronization signal detection device extracts a synchronization signal from the zero-crossing point of