GB1572539A

GB1572539A - Variable speed facsimile transmitter using storage mode photodetection array

Info

Publication number: GB1572539A
Application number: GB474778A
Authority: GB
Original assignee: Matsushita Graphic Communication Systems Inc; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic System Solutions Japan Co Ltd; Panasonic Holdings Corp
Priority date: 1977-02-07
Filing date: 1978-02-06
Publication date: 1980-07-30
Also published as: DE2804979B2; FR2379955A1; DE2804979A1; JPS5855712B2; JPS5397319A; FR2379955B1; DE2804979C3; CA1130443A

Description

(54) VARIABLE SPEED FACSIMILE TRANSMITTER USING STORAGE MODE PHOTODETECTION ARRAY (71) We, MATSUSHITA ELECTRIC INDUSTRIAL COMPANY. LIMITED and MATSUSHITA GRAPHIC COMMUNICATION SYSTEMS. INC.. corporations organized under the laws of Japan, of No. 1006, Oaza Kadoma, Kadoma City, Osaka and No.

2-3-X Shimomeguro Meguro-kuq 'I'okyos Japans respectively, do hereby declare the invention. for which we prav that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to facsimile communication and more specifically to a variable speed facsimile transmitter which employs a storage mode photodetection array as a means of deriving a video line sienal and method of operating the facsimile transmitter emplovine such photodeiection arravs.

The present invention incorporates self-scanning photodetection arravs as a means of sensing visual information recorded on a printed document to be transmitted over long distances. The photodetection arravs utilize solid state photosensitive devices which operate in a storage mode. These devices. when operated in the storage mode with a junction reverse biased. have the characteristics of a capacitor. When the junction is open circuited the junction slowly discharges as electrodes and holes are generated thermally and neutralize the stored charge On each side of the junction. With the application of light to the device, the chareine of the device occurs much more rapidlv and hence the device may be used to sense light. Typically. the device is discharged periodically and the discharging current is sensed: this current is a function of the total incident light on the device, i.e. the time integral of the incident light. In many pattern recognition applications which utilize an array of photodiodes in a storage ínode of operation. an elongated row of the photosensitive device is scanned electrically. Typically. the electrical circuit utilized to scan the photosensitive devices is incorporated on the same semiconductor substrate or chip as the photosensitive devices. The photodetection array incorporated in the present invention is commerciallv available from Reticon Corporation, U.S.A.

Because of the storage mode of operation with the magnitude of the available output varying as a function of the time integral of the quantity of incident light, and because of the possible difference between the scanning speed of the photosensitive device and the speed at which an electronic circuit processes the video signal into a format suitable for transmission, it is necessarv to drive the photosensitive device such that a same line path of a printed document is scanned repeatedly until the processor is readv to process the output of the photosensitive device. Otherwise, the photosensitive device would reach the saturation level upon prolonged exposure to the sensed line. This requires that the photosensitive device be repeatedly discharged at intervals.

In practice. facsimile communication systems are designed to operate on a number of transmission speeds to meet the users requirements. Where the aforesaid photodetection array is employed as a means of scanning documents, the amplitude of the scanner output will vlrv depending on the transmission speed.

To keep the video output constant over the differing transmission speeds, a prior art svstem. disclosed in Japanese Patent Application 51-1()5921, Iaid open to public inspection on September 17* 1()76 discharges the photodetection array at a constant frequency which is a common multiple of the different scanning frequencies of the system. For example, assume the system has 3Hz and 5Hz scanning frequencies, the photodetector is discharged llWaXS at 15Hz, regardless of the selected scanning frequencv.

However. since the amplitude of the photodetector output decreases with increasing discharge frequency, the video output of the prior art system is of small amplitude, which would require amplification of the signal or a high performance optical system to reduce the loss of incident light.

According to the present invention there is provided a variable speed facsimile transmitter including means for generating svnchronization pulses at one of a plurality of manually selectable rates, a storage mode photodetection array and means for driving said photodetection array in response to cinch of said sync pulses, comprising means for discharging said photodetection 'array nt an instant delayed from the time of occurrence of the sync pulse bv 'in interval (which m'ly be zero) dependent on the difference between the selected synchroniz'iiion rate and the highest one of the sync rates so that said photodetection array is wallowed to develop charges during a constant interval regardless of the sync pulse rate so selected.

Thus, in a facsimile transmitter which employs a storage mode photodetection array and drives it at one of i plurality of manually selectable clock rates the present invention contemplates to discharge the photodetection array at an instant of time which is delaved from the time of occurrence of the clock pulse by an interval responsive to the difference between the selected clock rate and the highest clock rate of the system so that the video signal available at the instant is discarded. Upon the discharge of the photodetection array, the array is allowed to develop charges for a constant time interval until the occurrence of a subsequent clock pulse. whereupon the array is energized to generate a video line signal having a constant amplitude regardless of the selected clock rate. Specifically, the interval is determined by counting a unit time period which is equal to the reciprocal of a common multiple of the selectable clock rates, and the discharge is effected when the count reaches a number determined bv the difference between the selected clock rate and the highest clock rate. Thus. there can be generated a video line signal of constant signal level from a storage mode photodetection array driven at variable clock rates regardless of the selected clock rate.

The present invention also provides. in another aspect, a method for operating a variable speed facsimile transmitter having a pluralitv of selectable line scaning frequencies tio provide different transmission speeds and a storage mode photodetection array adapted to generate a video line signal. comprising the steps of: a) generating sync pulses at a frequency corresponding to a selected one of said scanning frequencies: b) determining the difference if any between the period of the selected frequencv and the period of the highest one of said scanning frequencies: c) causing said photodetection array to discharge its stored electrical energy (i) at an instant delaved from the time of occurrence of the sync pulse by a time interval determined bv said difference in period of said scanning frequencies when the selected frequency is other than said highest frequencv or (ii) at the occurrence of the sync pulse when said highest frequency is selected: d) allowing said photodetection array to accumulate electrical charges after the e.nd of said time interval when the selected frequency is other than said highest frequency. or allowing said photodetection array to accumulate electrical charges after said sync pulse when said highest frequency is selected: and e) driving said photodetection array to generate said video line signal in response to each of said sync pulses.

The invention will be further described with reference to the accompanying drawings. in which: Fi, re I is a schematic block diagram of an exemplary embodiment of the invention: and Fi,loe is a timing diagram useful for describing the operation of Figure 1.

The facsimile transmitter of the present invention represented in Figure 1 of the drawings includes a 2,t)4X-bit storage mode photodiode array or detector 1() which is shown connected to a starting circuit 12 which energizes the detector to receive drive pulses from a source (not shown) of drive clock (Figure 2A) through a gate 14. The rate of this clock is so selected that the photodetector 1() completes its delivery of a line video output within the period of n synchroniz'ition pulse (Figure 'C) which appears at the start of each line scan.

The sync pulse is applied to an AND gate 16 to enable it to pass a discharge clock pulse (Figure 'D) used to discharge the photodiode array to reset it to the initial charge level. A 3,f)48-hit counter '.) is shown connected to the output of the gate 14 to count the number of clock pulses supplied to the photodetector 1(). Therefore, the flip-flop 18 will be reset in response to a pulse count of 2,t)4 bits by the output of the counter 9() to terminate the supply of clock pulses to the photodetector 1() (Figures'E. 2F and 'cm).

A video output is thus delivered from the photo-detector 1() and supplied to a first input of a comparator 22 for comparison with a reference voltage to eliminate anv ambiguous level signal components so that the comparator output is a clear-cut. black-and-white signal. This signal is clocked into a shift register 24 by the clock pulses passed through gate 14 and an OR gate 26.

A flip-flop 'X is shown connected to the output of counter 20 which triggers flip-flop 28 into a set condition upon the count of 2,048 pulses of drive clock. A gate 30 is shown connected to the Q output of the flip-clop 28 to pass discharge clock pulses on lead 32 to the photodetector l() in the presence of the high Q output state of flip-flop 28. The output circuit of the gate 3() is connected to an input of a programmable counter 34 which counts a predetermined number of input pulses to reset the flip-flop 28. The programmable counter 34 is so conditioned by means of a circuit designated by numeral 36 as to count as many discharge pulses to be applied to the photodetector 10 as necessary depending on the scanning frequency selected.

Assume that the system is capable of transmitting signals at one of a plurality of selectable transmission speeds which correspond to line scanning frequencies Fl, F2 .....

Fn where Fn is the maximum frequency. Each line path of document is transmitted at one of intervals Tl. T2 Tn which correspond to the cycle period of the frequencies Fl, F2 ..... Fn. respectively. Therefore, Tn is the minimum transmission interval of the system.

Consider now the minimum time interval necessary for the photodetector 1O to produce a video output of acceptable amplitude level, and let us designate this minimum interval Tmin.

This minimum interval Tmin may be equal to or smaller than the minimum transmission interval Tn of the system and the following relation can hold: N Tmin = M + N x Tn (1) where, M is an integer including zero and N is an integer at least unity.

Let Fcm denote a frequency which is a common multiple of the frequencies Fl. F2 .....

Fn. and let Fi denote any one of the frequencies Fl through Fn. In the present invention.

Fcm is equal to the frequency at which the photodetector 1() is discharged. i.e. discharge clock rate is equal to Fcm.

Therefore. the number of discharging operations that is required of the photodetector 10 before it starts to generate video signals is determined by the following Equation: K = Fcm N N Fem . (2) Fi M + N Fn For purposes of illustration. the system is assumed to have 3Hz and 5Hz scanning frequency modes so that Fcm is at 15Hz. i.e. the discharge clock rate is at 15Hz. Assume, for the sake of simplicitv, that M = 0. and that the system is operating in the 3Hz mode. it will be appreciated that the photodetector 10 is discharged "twice" bv the output from the gate 31).

The circuit 36 determines the K value that is used to program the counter 34 so that "two" discharge clock pulses may be passed through the gate 30 to the photodetector 10.

The circuit 36 is shown as comprising a division circuit 44 which performs division of an electrical value representing the frequency Fcm bv another electrical value representing a selected frequency Fi. A second division circuit 46 provides division of an electrical quantity representing Fcm by another quantitv representing Fn. The output of the division circuit 46 is multiplied in a multiplier 48 by a qu:intitv representing N/(M + N) provided from a source 50. The output from the multiplier 48 is used to subtract from the output of the division circuit 44 by means of a subtractor 52 to generate a substraction output which corresponds to the K value of Equation (2).

The programmable counter 34 is thus instructed to count two discharge pulses supplied from the output of gate 30 and reset the flip-flop 28 to terminate the supply of discharge clock to the photodetector 10 (see Figures 21, 23 and 2K).

In response to the absence of svnchronization pulses, gates 38 and 40 are activated to pass transmission clock pulses to the shift register 24 via OR gate 26 and clock out the video information now stored in the shift reeister via gate 4O to an utilization circuit (not shown) where the video signal will be processed into a form suitable for transmission.

If the system is switched to the 5Hz scanning mode. the programming circuit 36 generates a signal which instructs the counter 34 to immediately reset the flip-flop 28 and inhibit it from being set in response to the output from the 2,048-bit counter 20. Therefore, no discharging operations occur. With the system being switched to the 5Hz mode, the timing signal will be so automatically adjusted that the synchronization pulses occur at intervals smaller than for the 3Hz mode. The photodetector 10 thus operates to accumulate charge in response to each svnchlonization pulse.

WHAT WE CLAIM IS: 1. A variable speed facsimile transmitter including means for generating synchronization pulses at one of a plurality of manually selectable rates, a storage mode photodetection arrlv and means for driving said photodetection array in response to each of said sync pulses comprising means for discharging said photodetection array at an instant delayed from the time of occurrence of the sync pulse by an interval (which may be zero) dependent on the difference between the selected synchronization rate and the highest one of the sync nllcs so that said photodetection array is alliiwed to (levclip cli;irges during a constant interval regardless of the sync pulse rate so selected.

2. A variable speed facsimile transmitter as claimed in claim 1. wherein said time interval is an integral multiple of the reciprocal of a common multiple of said sync rates.

3. A variable speed facsimile transmitter as claimed in claim 2. wherein said common multiple is the least common multiple of said sync rates.

A. A variable speed facsimile transmitter as claimed in claim 1. 2 or 3, wherein said discharging means comprises means for generating clock pulses at a rate equ'il to a common multiple of said synchronization rates, means for counting said clock pulses to provide an output upon a count predetermined by said difference in sync rate, and means for applving said clock pulses to said photodetection array to discharge same for an interval from the occurrence of the sync pulse to the occurrence of said output from the counting means.

5. A variable speed facsimile transmitter as claimed in claim 4. wherein said counting means comprises a progr'tmmable counter.

6. A variable speed facsimile tr'insmitter as claimed in any preceding claim, wherein said discharging means includes me'ins for allowing said photodetection array to accumulate charges according to the light image applied after said instant of discharge when said selected sync rate is other than said highest sync rate, or in response to the time of occurrence of the sync pulse when said highest sync rate is selected.

7. A method for operating a variable speed facsimile transmitter having a plurality of selectable line scanning frequencies to provide different transmission speeds and a storage mode photodetection array adapted to generate a video line signal, comprising the steps of: a) generating sync pulses at a frequency corresponding to a selected one of said scanning trequencies: b) determining the difference if anv between the period of the selected frequencv and the period of the highest one of said scanning frequencies: c) causing said photodetection arrav to discharge its stored electrical energy (i) at an instant delaved from the time of occurrence of the sync pulse bv a time interval determined bv said difference in period of said scanning frequencies when the selected frequencv is other than said highest frequencv or (ii) at the occurrence of the sync pulse when said highest frequencv is selected: d) allowing said photodetection array to accumulate electrical charges after the end of said time interval when the selected frequency is other than said highest frequency. or allowing said photodetection array to accumulate electrical charges after said sync pulse when said highest frequency is selected: e) driving said photodetection array to generate said video line signal in response to each of said svnc pulses.

8. A method as claimed in claim 7. wherein said interval is an integral multiple of a reciprocal of a common multiple of said scanning frequencies.

9. A method as claimed in claim 7 or tA. wherein the discharging step comprises discharging said photodetection array one or more times at a frequencv equal to a common multiple of said scanning frequencies.

l. . A method as claimed in claim 9. wherein said common multiple is the least common multiple of said scanning frequencies.

11. A method of operating a variable speed facsimile transmitter having a storage mode photodetection array and means for driving said array at one of a pluralitv of selectable line scanning frequencies F,. F2 ..... Fn where F" is the highest frequency. comprising: dividin a time interval T which corresponds to the reciprocal of said highest frequency F" into (NI + N) equal time segments. where M is an integer inclusive of zero and N is an integer exclusive of zero: multiplying said interval T by N M + N) to derive a minimum time interval This necessary to obtain a video signal of an acceptable signal level: dividing a time interval T1 which corresponds to the reciprocal of a selected line scanning frequency into a first section (which may be zero) in which said photodetection array is prevented from deriving said video signal and a second section equal to said minimum time interval T

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. smaller than for the 3Hz mode. The photodetector 10 thus operates to accumulate charge in response to each svnchlonization pulse. WHAT WE CLAIM IS:

1. A variable speed facsimile transmitter including means for generating synchronization pulses at one of a plurality of manually selectable rates, a storage mode photodetection arrlv and means for driving said photodetection array in response to each of said sync pulses comprising means for discharging said photodetection array at an instant delayed from the time of occurrence of the sync pulse by an interval (which may be zero) dependent on the difference between the selected synchronization rate and the highest one of the sync nllcs so that said photodetection array is alliiwed to (levclip cli;irges during a constant interval regardless of the sync pulse rate so selected.

l.ì. A method as claimed in claim 9. wherein said common multiple is the least common multiple of said scanning frequencies.

11. A method of operating a variable speed facsimile transmitter having a storage mode photodetection array and means for driving said array at one of a pluralitv of selectable line scanning frequencies F,. F2 ..... Fn where F" is the highest frequency. comprising: dividin a time interval T which corresponds to the reciprocal of said highest frequency F" into (NI + N) equal time segments. where M is an integer inclusive of zero and N is an integer exclusive of zero: multiplying said interval T by NíM + N) to derive a minimum time interval This necessary to obtain a video signal of an acceptable signal level: dividing a time interval T1 which corresponds to the reciprocal of a selected line scanning frequency into a first section (which may be zero) in which said photodetection array is prevented from deriving said video signal and a second section equal to said minimum time interval T

determining the first section by counting a unit time interval equal to the reciprocal of a common multiple of said scanning frequencies a number of times equal to N (Fcm/Fi - x Fcm/Fn N + M where Fel,l is said common multiple. and Fi is the selected frequencv: and allowing said photodetection array to develop charges during said minimum time interval T"" to derive solid video signal at the end of said minimum time interval.

12. A method as claimed in claim I I wherein said common multiple is the least common multiple of said scanning frequencies.

13. A variable speed facsimile transmitter constructed and arrangcd substantially as described herein with reference to the accompanying drawings.

14. A method of operating a variable speed facsimile transmitter substantially as hereinbefore described with reference to the accompanying drawings.