JPS6234311B2 - - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a device that adjusts the amount of illumination light and reads information in a band where the linearity of the image signal level is good.

Background of the Technology Cameras used to capture images for reading patterns and classifying their signal levels to obtain information use image pickup tubes or solid-state image pickup devices. The relationship between the brightness of the object surface and the amplitude of the camera output signal is not good, as shown in FIG. This is because current cameras can only provide output that is linear with respect to changes in brightness that are approximately four times as large. There is almost no difference in the signal output when it is a little darker than weak brightness level 1 and when it is a little brighter, and the amplitude is relatively large where it should be small (the broken line in Figure 2 A). (solid line in Figure 2 A). In the case of brightness level 4, the tendency for the amplitude to become relatively small is similar (solid line in FIG. 2C). In areas with good linearity, there is no difference between the solid line and the broken line, as shown in FIG. 2B.

Prior Art and Problems When it is determined that an object is illuminated with such brightness that linear output cannot be obtained, two methods have been conventionally adopted for feedback processing to deal with the problem. The first is to control the light source to brighten or darken it so that it falls within the linear output range. At this time, with a light source using a normal incandescent bulb, the response is slow and takes 0.1 to 1 second. As a result, it was not possible to capture images with movement such as pattern scanning. The second method is to control the level interval for dividing the output amplitude of the camera output signal according to the illuminance. Although the output obtained by this means can be adjusted relatively precisely, the equipment is extremely complex and expensive.

OBJECTS OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks and to provide a device that has a simple configuration and reads information in a band where the linearity of the video signal level is good.

Configuration of the Invention The configuration of the present invention provides a video information reading device that A/D converts and reads the video output of a camera that images an object illuminated by a light source. A light source switching circuit for switching on/off of the light emitting diodes, as many illumination light amount adjustment circuits as the number of light emitting diodes, and a circuit for maintaining the peak value of the video output, and the light emitting diodes used according to the imaged portion of the object. is selected by the light source switching circuit, and the output of the peak value holding circuit is compared with a reference value, and the signal output of the difference is used to control the illumination light amount adjustment circuit to maintain the peak value of the video output constant. It is.

Embodiments of the Invention Examples of the present invention shown in the drawings will be described below. FIG. 3 is a configuration diagram showing an embodiment of the present invention, in which LLC is a lighting light amount adjustment circuit, LCC is a light source switching control circuit, LPW is a light source power supply circuit, LED is a light emitting diode for lighting, and TV-CM is a TV camera. , TV−
DV is a TV driver, VDH is a video signal peak value holding circuit, A/D-C is a multilevel conversion circuit, PMM is an image memory, CT is a control system, and RCN is a recognition system.
The light source switching control circuit LCC selects which light emitting diode LED to use for lighting, and controls the light source power supply circuit LPW. Obtain the output of the peak value holding circuit VDH for the output of TV-Camera TV-CM,
It is applied to the illumination light amount adjustment circuit LLC to control the light source power supply circuit LPW. FIG. 4 shows an example of the configuration of the illumination light amount adjustment circuit LLC. The output image of the TV camera has approximately 500 rasters as one frame, and the output waveform of each raster is as shown in FIG. For each raster, the amplitude peak value AM1 or AM2 is extracted by the peak value holding circuit VDH, and its output is compared with the reference value Vrf in the illumination light amount adjustment circuit LLC. At that time, the value of Vrf is, for example, the voltage corresponding to the brightness level 2.5 in Figure 1,
The difference with the peak value holding circuit VDH is calculated by the operational amplifier OP. The output is amplified by transistor TR,
Light-emitting diode LED for lighting emits light. TV camera → Peak value holding circuit VDH → Light intensity adjustment circuit
LLC → Light source power supply circuit LPW → Light emitting diode LED
The circuit forms a feedback control circuit. The response speed of light emitting diodes LED is extremely fast compared to incandescent light bulbs, so the peak value holding circuit VDH is shown in Figure 5 AM.
1, AM2... It can respond every time it changes, and the brightness of the light source can be controlled.

Effects of the Invention As described above, according to the present invention, even when the illumination changes every short time, it can be controlled using light emitting diodes without delay in response. It is possible to operate with the output signal level within a band with good linearity.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the relationship between video camera output signal amplitude and brightness, Fig. 2 is a diagram of typical output amplitude, Fig. 3 is a configuration diagram of an embodiment of the present invention, and Fig. 4 is a diagram of the illumination in Fig. 3. FIG. 5 is a diagram showing an example of the configuration of a light amount adjustment circuit, and FIG. 5 is a diagram showing an output waveform of a TV camera. LLC...Lighting light amount adjustment circuit, LED...Light emitting diode, LCC...Light source switching control circuit, LPW...
...Light source power supply circuit, TV-CM...TV camera, VDH
...Video signal peak value holding circuit.

Claims (1)

[Scope of Claims] 1. A video information reading device that A/D converts and reads the video output of a camera that images an object illuminated by a light source, comprising: a plurality of light emitting diodes as light sources; It is equipped with a light source switching circuit that switches on and off, an illumination light intensity adjustment circuit of the same number as the light emitting diodes, and a circuit that maintains the peak value of the video output, and the light emitting diodes to be used according to the imaged part of the object are adjusted. the light source switching circuit, and comparing the output of the peak value holding circuit with a reference value, controlling the illumination light amount adjustment circuit based on the signal output of the difference, and maintaining the peak value of the video output constant. A video information reading device characterized by: