1. A multi-color image forming apparatus comprising:
a plurality of color image forming units adapted to form a plurality of different color images;
a transfer belt to which positioning color image patterns are transferred by said color image forming units;
an optical sensor adapted to detect said positioning color image patterns;
a positioning color image pattern trailing edge detecting circuit adapted to detect trailing edges of said positioning color image patterns by determining that an output signal of said optical sensor has reached a threshold value, said threshold value being a predetermined ratio of a peak value of the output signal of said optical sensor; and
a control circuit adapted to compensate for registration of said color image forming units in accordance with the detected trailing edges of said positioning color image patterns.
2. The multi-color image forming apparatus as set forth in claim 1, wherein, when a first one of said positioning color image patterns has a larger reflectance for an emitted light from said optical sensor than a predetermined value, said first positioning color image pattern is of a single structure,
when a second one of said positioning color image patterns has a smaller reflectance for the emitted light from said optical sensor than said predetermined value, said second positioning color image pattern is of a double structure of said second positioning color image pattern underlying a third positioning color image pattern which has a larger reflectance for the emitted light from said optical sensor than said predetermined value,
said second positioning color image pattern having a leading edge retarded from a leading edge of said third positioning color image pattern with respect to a direction of propagation of said transfer belt.
3. The multi-color image forming apparatus as set forth in claim 2, wherein, said second positioning color image pattern has a trailing edge forwarded from a leading edge of said third positioning color image pattern with respect to the direction of propagation of said transfer belt.
4. The multi-color image forming apparatus as set forth in claim 2, wherein, said second positioning color image pattern has a trailing edge located at a leading edge of said third positioning color image pattern with respect to the direction of propagation of said transfer belt.
5. The multi-color image forming apparatus as set forth in claim 1, wherein said color image forming units are a magenta image forming unit, a cyan image forming unit, a yellow image forming unit and a black image forming unit,
said magenta image forming unit transferring first and second positioning magenta toner patterns to said transfer belt,
said cyan image forming unit transferring a positioning cyan toner pattern underlying said second magenta toner pattern to said transfer belt, said positioning cyan toner pattern having a leading edge retarded from a leading edge of said second magenta toner pattern with respect to a direction of propagation of said transfer belt,
said yellow image forming unit transferring first and second positioning yellow toner patterns to said transfer belt,
said black image forming unit transferring a positioning black toner pattern underlying said second yellow toner pattern to said transfer belt, said positioning black toner pattern having a leading edge retarded from a leading edge of said second yellow toner pattern with respect to a direction of propagation of said transfer belt.
6. The multi-color image forming apparatus as set forth in claim 5, wherein said positioning cyan toner pattern has a trailing edge forwarded from a trailing edge of said second magenta toner pattern with respect to the direction of propagation of said transfer belt, and
wherein said positioning black toner pattern has a trailing edge forwarded from a trailing edge of said second yellow toner pattern with respect to the direction of propagation of said transfer belt.
7. The multi-color image forming apparatus as set forth in claim 5, wherein said positioning cyan toner pattern has a trailing edge located at a trailing edge of said second magenta toner pattern with respect to the direction of propagation of said transfer belt, and
wherein said positioning black toner pattern has a trailing edge located at a trailing edge of said second yellow toner pattern with respect to the direction of propagation of said transfer belt.
8. The multi-color image forming apparatus as set forth in claim 1, wherein said color image forming units are a magenta image forming unit, a cyan image forming unit, a yellow image forming unit and a black image forming unit,
said magenta image forming unit transferring first and second positioning magenta toner patterns to said transfer belt,
said yellow image forming unit transferring first and second positioning yellow toner patterns to said transfer belt,
said cyan image forming unit transferring a positioning cyan toner pattern underlying said second yellow toner pattern to said transfer belt, said positioning cyan toner pattern having a leading edge retarded from a leading edge of said second yellow toner pattern with respect to a direction of propagation of said transfer belt,
said black image forming unit transferring a positioning black toner pattern underlying said second magenta toner pattern to said transfer belt, said positioning black toner pattern having a leading edge retarded from a leading edge of said second magenta toner pattern with respect to a direction of propagation of said transfer belt.
9. The multi-color image forming apparatus as set forth in claim 8, wherein said positioning cyan toner pattern has a trailing edge forwarded from a trailing edge of said second yellow toner pattern with respect to the direction of propagation of said transfer belt, and
wherein said positioning black toner pattern has a trailing edge forwarded from a trailing edge of said second magenta toner pattern with respect to the direction of propagation of said transfer belt.
10. The multi-color image forming apparatus as set forth in claim 8, wherein said positioning cyan toner pattern has a trailing edge located at a trailing edge of said second yellow toner pattern with respect to the direction of propagation of said transfer belt, and
wherein said positioning black toner pattern has a trailing edge located at a trailing edge of said second magenta toner pattern with respect to the direction of propagation of said transfer belt.
11. The multi-color image forming apparatus as set forth in claim 1, wherein said optical sensor comprises:
alight emitting portion for emitting light; and
a light receiving portion adapted to receive reflected light of said emitted light from said positioning color image patterns,
a plane including an optical axis of said light emitting portion and an optical axis of said light receiving portion being perpendicular to a direction of propagation of said transfer belt and being inclined toward the direction of propagation of said transfer belt.
12. The multi-color image forming apparatus as set forth in claim 11, wherein said light emitting portion generates a single polarized component and said light receiving portion receives a polarized component different from said single polarized component.
13. The multi-color image forming apparatus as set forth in claim 1, wherein said positioning color image pattern trailing edge detecting circuit comprises:
a peak hold circuit adapted to hold said peak value of the output signal of said optical sensor;
a voltage divider connected to said peak hold circuit and adapted to divide said peak value to generate said threshold value;
a comparator connected said voltage divider and adapted to compare the output signal of said optical sensor with said threshold value to generate a comparison signal for showing the trailing edges of said positioning color image patterns;
a reset signal generating circuit connected to said comparator and adapted to delay said comparison signal by a predetermined delay time period to generate a reset signal; and
a reset circuit connected between said reset signal generating circuit and said peak hold circuit and adapted to reset said peak hold circuit in accordance with said reset signal.
14. The multi-color image forming apparatus as set forth in claim 13, wherein said peak value is a maximum value of the output signal of said optical sensor.
15. The multi-color image forming apparatus as set forth in claim 13, wherein said peak value is a minimum value of the output signal of said optical sensor.
16. A method for detecting positioning color image patterns in a multi-color image forming apparatus comprising:
a plurality of color image forming units adapted to form a plurality of different color images;
a transfer belt to which positioning color image patterns are transferred by said color image forming units; and
an optical sensor adapted to detect said positioning color image patterns,
said method comprising:
holding said peak value of the output signal of said optical sensor;
dividing said peak value to generate said threshold value;
determining whether or not the output signal of said optical sensor has reached said threshold value;
determining detection of a trailing edge of the output signal of said optical sensor and resetting said peak value and said threshold value when it is determined that the output signal of said optical sensor has reached said threshold value.
17. The method as set forth in claim 16, wherein said peak value is a maximum value of the output signal of said optical sensor.
18. The method as set forth in claim 16, wherein said peak value is a minimum value of the output signal of said optical sensor.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A timing synchronous detection device comprising:
a first autocorrelator that performs autocorrelation using a received signal and a first delay signal in which the received signal is delayed;
a second autocorrelator that performs autocorrelation using the received signal and a second delay signal in which the received signal is delayed;
an average-normalization device that obtains an average value of an output signal of the first autocorrelator and an output signal of the second autocorrelator;
a comparator that compares the average value and a threshold value and that outputs, if the average value is larger than the threshold value, the average value; and
a maximum value search device that searches for a maximum value of average values that are output from the comparator.
2. The timing synchronous detection device of claim 1, wherein the received signal is a preamble, and the first delay signal is a signal that is delayed by a half of a size of the preamble.
3. The timing synchronous detection device of claim 2, wherein the preamble comprises a cyclic prefix, a first effective symbol segment, and a second effective symbol segment having a same size as that of the first effective symbol segment, and the first autocorrelation is performed between the cyclic prefix with a last segment of the first effective symbol segment and the second autocorrelation is performed between the cyclic prefix with a last segment of the second effective symbol segment.
4. The timing synchronous detection device of claim 3, wherein the first autocorrelator comprises:
a delay device that generates the first delay signal;
a first cumulative device that accumulates a multiplication result of the first delay signal and the received signal by a cyclic prefix length;
a first calculator that calculates an absolute value of an output result from the first cumulative device;
a square device that calculates a square value of an output result from the first calculator;
a first energy calculator that calculates energy of the first delay signal;
a second energy calculator that calculates energy of the received signal;
a second cumulative device that accumulates a sum result of an output result of the first energy calculator and an output result of the second energy calculator;
a second calculator that calculates a reciprocal of an output result from the second cumulative device; and
a multiplication device that multiplies an output result of the square device and an output result of the second calculator and that outputs an output result as an output result of the first autocorrelator.
5. The timing synchronous detection device of claim 4, further comprising a conjugate converter that generates a conjugate of the first delay signal and that outputs the conjugate to multiply the received signal by the conjugate.
6. The timing synchronous detection device of claim 1, wherein the received signal is a preamble, and the second delay signal is a signal that is delayed by a size of the preamble.
7. The timing synchronous detection device of claim 6, wherein the preamble comprises a cyclic prefix, a first effective symbol segment, and a second effective symbol segment having a same size as that of the first effective symbol segment, and the first autocorrelation is performed between the cyclic prefix with a last segment of the first effective symbol segment and the second autocorrelation is performed between the cyclic prefix with a last segment of the second effective symbol segment.
8. The timing synchronous detection device of claim 7, wherein the second autocorrelator comprises:
a delay device that generates the second delay signal;
a first cumulative device that accumulates a multiplication result of the second delay signal and the received signal by a cyclic prefix length;
a first calculator that calculates an absolute value of an output result from the first cumulative device;
a square device that calculates a square value of an output result from the first calculator;
a first energy calculator that calculates energy of the second delay signal;
a second energy calculator that calculates energy of the received signal;
a second cumulative device that accumulates a sum result of an output result of the first energy calculator and an output result of the second energy calculator;
a second calculator that calculates a reciprocal of an output result from the second cumulative device; and
a multiplication device that multiplies an output result of the square device and an output result of the second calculator and that outputs an output result as an output result of the first autocorrelator.
9. The timing synchronous detection device of claim 8, further comprising a conjugate converter that generates a conjugate of the second delay signal and that outputs the conjugate to multiply the received signal by the conjugate.
10. A method in which a timing synchronous detection device detects timing synchronization using a received signal, the method comprising:
performing first autocorrelation using the received signal and a first delay signal in which the received signal is delayed;
performing second autocorrelation using the received signal and a second delay signal in which the received signal is delayed;
obtaining an average value of a result of the first autocorrelation and a result of the second autocorrelation;
comparing the average value and a threshold value; and
searching for, if the average value is larger than the threshold value, a maximum value of the average values.
11. The method of claim 10, wherein the received signal is a preamble, and the first delay signal is a signal that is delayed by a half of a size of the preamble.
12. The method of claim 11, wherein the preamble comprises a cyclic prefix, a first effective symbol segment, and a second effective symbol segment having a same size as that of the first effective symbol segment, and the first autocorrelation is performed between the cyclic prefix with a last segment of the first effective symbol segment and the second autocorrelation is performed between the cyclic prefix with a last segment of the second effective symbol segment.
13. The method of claim 12, wherein the performing of first autocorrelation comprises:
generating the first delay signal by delaying the received signal by a half of the size of the preamble;
multiplying the first delay signal and the received signal;
accumulating a cyclic prefix length to a multiplied result of the first delay signal and the received signal and outputting the cumulative result as a first cumulative result; and
calculating power of the first cumulative result.
14. The method of claim 13, wherein the calculating of power comprises:
calculating an absolute value of the first cumulative result; and
obtaining a square value of the absolute value.
15. The method of claim 14, wherein the performing of first autocorrelation further comprises:
calculating energy of the received signal and the first delay signal, adding the calculated energies, and outputting the added calculated energy as a first sum; and
accumulating the first sum and outputting the accumulated first sum as a third cumulative result.
16. The method of claim 15, wherein the performing of first autocorrelation further comprises
dividing the power of the first cumulative result by the third cumulative result and outputting the divided power of the first cumulative result as a result of the first autocorrelation.
17. The method of claim 11, wherein the second delay signal is a signal that is delayed by the size of the preamble, and
the preamble comprises a cyclic prefix, a first effective symbol segment, and a second effective symbol segment having a same size as that of the first effective symbol segment, and the first autocorrelation is performed between the cyclic prefix with a last segment of the first effective symbol segment and the second autocorrelation is performed between the cyclic prefix with a last segment of the second effective symbol segment.
18. The method of claim 17, wherein the performing of second autocorrelation comprises:
generating the second delay signal by delaying the received signal by the size of the preamble;
multiplying the second delay signal and the received signal;
accumulating a cyclic prefix length to a multiplied result of the second delay signal and the received signal and outputting the cumulative result as a second cumulative result; and
calculating power of the second cumulative result.
19. The method of claim 18, wherein the calculating of power comprises:
calculating an absolute value of the second cumulative result; and
obtaining a square value of the absolute value.
20. The method of claim 18, wherein the performing of second autocorrelation further comprises:
calculating energy of the received signal and the second delay signal, adding the calculated energies, and outputting the added calculated energy as a second sum; and
accumulating the second sum and outputting the accumulated second sum as a fourth cumulative result.