Image reading device

Abstract

To make it possible to adjust more precisely (seamlessly) the lighting time of an illumination light source on an image reading device.SOLUTION: When a lighting period of illumination means in each reading cycle on each line of a document to be read is divided into N sub-lighting periods, the number of sub-lighting periods N that constitutes a lighting period and start timing of each sub-lighting period are determined so that an average frequency of the clock signal in each sub-lighting period and an average frequency of the clock signal that is frequency modulated by spectrum spreading means are equal.SELECTED DRAWING: Figure 5

Claims

1. A lighting means that illuminates the document by turning on a light source, A reading means for reading a document illuminated by the aforementioned illumination means, A generating means for generating a clock signal that serves as a reference for the lighting time of the aforementioned lighting means, A spread spectrum means for frequency modulating the frequency of the clock signal with a predetermined modulation period, The system includes a control means that controls the illumination means and the reading means based on a clock signal frequency-modulated by the spread spectrum means, The control means is An image reading device characterized in that, when the illumination period of the illumination means in each reading cycle when reading the document line by line is divided into N sub-illumination periods, the number of sub-illumination periods constituting the illumination period and the start timing of each sub-illumination period are determined so that the average frequency of the clock signal in each sub-illumination period matches the average frequency of the clock signal frequency-modulated by the spread spectrum means.

2. The image reading device according to claim 1, characterized in that the time from the start timing of the first sub-lighting period among the N sub-lighting periods to the end timing of the Nth sub-lighting period is longer than half a period of the modulation period.

3. Each reading cycle contains M half-cycles of the modulation cycle, with reference to the start timing of the first sub-lighting period (M ≥ N). The aforementioned N sub-lighting periods are included in one of the aforementioned M half-cycles, The image reading device according to claim 2, characterized in that the same lighting pattern applied to the odd-numbered half-periods among the M half-periods is also applied to the even-numbered half-periods, and the lighting pattern indicates the length of the sub-lighting period.

4. The image reading device according to claim 1, characterized in that the number N of the sub-lighting periods is even, and the start timing of each sub-lighting period has a certain periodicity.

5. The image reading device according to claim 4, characterized in that the time difference between the start timing of the i-th sub-lighting period and the start timing of the (i+1)-th sub-lighting period among the N sub-lighting periods is equal to half a period of the modulation period.

6. The first lighting pattern applied to the first odd-numbered half-period among the M half-periods is also applied to the first even-numbered half-period. The image reading device according to claim 3, characterized in that the second lighting pattern applied to the second odd-numbered half-period among the M half-periods is also applied to the second even-numbered half-period.

7. The image reading device according to claim 3, characterized in that the lighting pattern is a pattern in which the illumination means is lit multiple times within the half-cycle.

8. The first odd-numbered half-period and the second odd-numbered half-period are adjacent to each other. The first lighting pattern is a pattern in which the lighting means is continuously lit for the entirety of the first odd-numbered half-cycle, The image reading device according to claim 6, characterized in that the second lighting pattern is a pattern in which the lighting means is lit for a time shorter than the second odd-numbered half-cycle.

9. The image reading device according to claim 6, characterized in that the first even-numbered half-period and the second even-numbered half-period are the same half-period.

10. The control means is Based on the reading period, the modulation period, and the illumination period, it is determined whether the illumination period can be divided. If the aforementioned lighting period can be divided, the aforementioned lighting period is divided into the N sub-lighting periods, The image reading device according to any one of claims 1 to 9, characterized in that, if the lighting period cannot be divided, the lighting period is reduced to another lighting period that is an integer J multiple of half a period of the modulation period, and the drive current supplied to the light source of the illumination means is increased from a first drive current to a second drive current.

11. The image reading device according to claim 10, characterized in that the integer J is the largest integer such that the other lighting period does not exceed the lighting period.

12. The image reading device according to claim 10, characterized in that the product of the lighting period and the first drive current is equal to the product of the other time and the second drive current.

13. The image reading device according to claim 10, characterized in that the control means determines that division is not possible if the time from the start timing of the first sub-lighting period among the N sub-lighting periods to the end timing of the lighting of the Nth sub-lighting period is longer than the reading cycle.

14. The lighting means has a plurality of light sources that can be individually lit, The control means determines whether the lighting period of each of the plurality of light sources can be divided, and if it determines that the lighting period of the first light source, which is the longest lighting period among the plurality of light sources, cannot be divided, it reduces the longest lighting period to another lighting period that is an integer J multiple of the half-cycle, increases the drive current supplied to the light source of the illumination means from the first drive current to the second drive current, reduces the lighting period of the second light source, which is different from the first light source among the plurality of light sources, by the same reduction rate as the reduction rate of the lighting period of the first light source, and divides the reduced lighting period of the second light source into N sub-lighting periods, as described in 10.

15. The image reading device according to claim 1, characterized in that the control means divides the illumination period into N sub-illumination periods when the illumination period is arranged such that the center of the illumination period is located at the phase in which the frequency of the clock signal is maximum, and the center of the illumination period is located at the phase in which the frequency of the clock signal is minimum, if the frequency difference between these two values ​​exceeds an allowable value.

16. A lighting means that illuminates the document by turning on a light source, A reading means for reading a document illuminated by the aforementioned illumination means, A clock supply means that supplies a clock signal that serves as a reference for the illumination period of the lighting means, A spread spectrum means for frequency modulating the frequency of the clock signal with a predetermined modulation period, A control method for an image reading device, comprising: a control means for controlling the illumination means and the reading means based on a clock signal frequency-modulated by the spread spectrum means, A control method for an image reading device, characterized in that, when the illumination period of the illumination means in each reading cycle when reading the document line by line is divided into N sub-illumination periods, the number of sub-illumination periods constituting the illumination period and the start timing of each sub-illumination period are determined so that the average frequency of the clock signal in each sub-illumination period matches the average frequency of the clock signal frequency-modulated by the spread spectrum means.

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