a preferred embodiment of the present invention is described with referenceto the accompanying drawings . a remote supervisory system which includes an embodiment of the present invention is described . the system comprises copying apparatuses , data terminals , a communication network and a center ( central supervisory apparatus ). fig1 is an illustration of the system . fig2 and 3 are block diagrams of the circuitry of the system . the system comprises apparatuses of users &# 39 ; side ( one of the users &# 39 ; apparatuses is shown in the drawings ), a central supervisory apparatus ( center ), and a communication network which connectsthe users &# 39 ; apparatuses to the center . each apparatus of the users &# 39 ; side comprises a copying machine 4 , a data terminal 1 which collects data about the condition of the copying machine 4 , a modem 52 which acts as a communication terminal for calling up a modem 72 of the center , and an ordinary telephone 53 which the modem 52 isattached to . the center comprises a computer 90 incorporating a cpu 91 , a modem 72 whichacts as a communication terminal for calling up the modems 52 of the users &# 39 ; apparatuses by order of the computer 90 , and an ordinary telephone 73 whichthe modem 72 is attached to . a hard disc 97 , a display 92 , a keyboard 93 and a printer 94 are connected to the cpu 91 . the data terminal 1 of the user &# 39 ; s apparatus reads data ( count data and element data shown in fig1 ) about the condition of the copying machine 4 , processes the data , and stores the processed data in an sram 15 . then , the data terminal 1 transmits the data to the computer 90 of the center regularly ( at intervals of a specified time and at intervals of a specified number of copies ) and also on occasions of trouble . the computer 90 of the center stores data transmitted from the data terminals 1 of the users &# 39 ; apparatuses in the hard disc 97 , and carries outprocessing for managing the copying machines 4 based on the data transmitted from the respective data terminals 1 . for example , based on the number of copies , the computer 90 calculates the copy fee . when receiving data indicating trouble , the computer 90 informs the user of theestimated time of sending a serviceman and gives a serviceman instructions . the copying machine 4 scans an original to make copies thereof . in the copying machine 4 , sensors 46 disposed in various portions detect matters which influence the copying process as element data , such as the copy sheet traveling time , the surface potential of the photosensitive drum , the toner density in the developer , the developing bias voltage , thevolume of toner stuck on the photosensitive drum and the grid voltage of the charger . the sensors 46 also detect trouble to be checked by a serviceman as trouble data , such as the end of the life of the exposure lamp , poor fixation , the end of the life of the heater and abnormal discharge of the charge wire . these data are taken in a cpu 41 of the copying machine 4 and processed therein , and the data are transmitted to acpu 11 of the data terminal 1 through serial interfaces 43 and 13 . also , in the cpu 41 , counter values which become a base of calculation of the copy fee in the center and counter values which become a base of maintenance are read out . the counters for the former purpose are a total copy counter which count all the ejected copy sheets and copy counters by size which count used copy sheets of the respective sizes . the counters for the latter purpose are jam counters by portion which count occurrencesof sheet jamming in the respective portions , trouble counters by portion which count occurrences of trouble in the respective portions and pm counters by part which count times of use of the respective parts . the read counter values are transmitted to the cpu 11 of the data terminal 1 as count data through serial interfaces 42 and 12 . the cpu 41 of the copying machine 4 also receives signals from key switchesprovided on an operation panel 40 ( see fig4 ), such as a print key 40a fora start of copying operation , a ten - key 40b for input of numbers , a clear / stop key 40c for a clear of input and a stop of copying operation , and function keys 40d , etc ., and from other switches , such as a trouble reset switch 45 , and in accordance with the signals , the cpu 41 controls the operation and the mode of the copying machine 4 . from the cpu 41 , signals for driving a liquid crystal display panel 400 on the operation panel 40 are sent out . the display panel 400 is divided intoa message block 400x , a copy mode block 400y and a multi - function block 400z . the message block 400x displays the state of the copying machine 4 , such as whether copying operation is possible or impossible , and emptinessof paper and / or toner . the copy mode block 400y displays the set conditionsof the copying operation , such as the number of copies , the sheet size , thecopy density , the copy magnification , the copy create , etc . the multi - function block 400z is for interactive setting of the automatic sheet selection , the automatic magnification selection , the zoom magnification selection , the create and the density , etc . by use of the function keys 40d . the message block 400x also displays the action of the modem 52 of the data terminal 1 and messages from the center when trouble occurs . a ram 44 is connected to the cpu 41 and is stored with the model number andthe serial number of the copying machine 4 , which are input at the time of shipment from the factory . then , when the data terminal 1 is installed , the cpu 41 transmits the model number and the serial number to the cpu 11 of the data terminal 1 through the serial interfaces 42 and 12 by a request of the cpu 11 . the ram 44 is also stored with words to be displayed in the message block 400x . the data terminal 1 receives data from the copying machine 4 connected thereto and processes the data . when it comes to one of predetermined cases to communicate with the center , for example , when it becomes a predetermined time , when the number of copies becomes a predetermined number , or when trouble occurs , the data terminal 1 drives the modem 52 toreach the communication line of the center and transmits data about the condition of the copying machine 4 ( element data , count data , trouble data , etc .) to the cpu 91 of the center . the cpu 11 of the data terminal 1 is connected to the modem 52 which acts as a communication terminal by communication interfaces ( rs232c ) 18 and 51 , and the modem 52 can be connected to the modem 72 of the center by a telephone line . the contents of the data transmitted from the cpu 11 to the cpu 91 of the center depend on the case . for example , when trouble occurs , data which indicate the kind of the trouble , etc . are transmitted . when the data terminal 1 is installed , identification data of the copying machine 4 ( themodel number and the serial number ) and of the data terminal 1 are transmitted . in regular data transmission which is carried out at intervals of a specified time and at intervals of a specified number of copies , element data and count data are transmitted . a rom 14 which is stored with control programs , a battery backup type sram 15 which is to be stored with identification data , trouble data , element data and count data , and a battery backup type internal clock 17 are connected to the cpu 11 . the cpu 11 is connected to the cpu 41 of the copying machine 4 by the connections between the serial interfaces 12 and 42 and between the serial interfaces 13 and 43 , and thereby , the cpu 11 can receive data from the cpu 41 . the cpu 11 has a push switch 21 and fourdip switches ( dip . sw1 , dip . sw2 . dip . sw3 , dip . sw4 ). these switches will be described in detail later . the cpu 91 is the main component of the computer 90 . the modem 72 is attached to the cpu91 by a connection between a communication interface ( rs232c ) 71 of the modem 72 and a communication interface ( rs232c ) 98 of the cpu 91 , and the modem 72 acts as a communication terminal . this computer 90 monitors a lot of copying machines 4 through the respective data terminals 1 . from the data terminals 1 of the users &# 39 ; apparatuses , element data , count data and trouble data , etc . are transmitted to the modem 72 via the communication network , and the data are sent to the cpu 91 through the communication interfaces ( rs232c ) 71 and 98 . the cpu 91 processes the data . supervisory data about the respective copying machines 4 are made , and the data are stored in the respective areas of the hard disc 97 . at the end of every month , the amounts of moneyto be charged the users are calculated from the data , and bills are printedout . in periodic communication ( regular communication at intervals of a specified time ) or copy number communication ( regular communication at intervals of a specified number of copies ) with a user , the cpu 91 sends the time of next periodic communication or the copy number of next copy number communication to the data terminal 1 of the user . in communication with a user at a time of trouble , the cpu 91 informs the user of the estimated time of sending a serviceman and gives instructions ( visiting time , parts to be carried , etc .) to a serviceman . the control of the system is described with reference to the processing of the cpu 41 and the processing of the cpu 11 . fig5 is a flowchart of a procedure carried out by the cpu 41 of the copying machine 4 . the procedure starts , for example , at a time of turning on the copying machine 4 . first , the memories are cleared , and initialization is carried out at step s41 . thereafter , loop processing after step s42 is carried outrepeatedly . step s42 is a step of receiving input signals . the input signals are , for example , signals entered by use of the key switches on the operation panel40 , signals sent from trouble sensors provided in various portions of the copying machine 4 , and signals sent from the cpu 11 . step s43 is a step ofdisplaying the state of the copying machine 4 , the operation mode , etc . on the display panel 400 of the operation panel 40 . while the copying machine 4 is operating to make copies (&# 34 ; yes &# 34 ; at step s44 ), the cpu 41 carries out necessary processing for copying operation atstep s45 . the processing carried out at step s45 includes sheet feeding , scanning control , and control of image forming elements such as the photosensitive drum and the developing device . further , every time a processed sheet is ejected from the copying machine 4 , element data and count data are transmitted to the cpu 11 . when a sheet jam or some other trouble ( the end of the life of the exposurelamp , poor fixation , the end of the life of the heater , abnormal discharge from the charge wire , etc .) occurs (&# 34 ; yes &# 34 ; at step s46 ), a trouble code which indicates the kind of the trouble is transmitted to the cpu 11 at step s47 . then , the cpu 11 transmits the trouble code to the center . at step s48 , messages about the trouble are displayed in the message block 400x of the display panel 40 . first , a message , &# 34 ; trouble has occurred &# 34 ; is displayed . then , when the data terminal 1 actuates the modem 52 , a message , &# 34 ; the machine is reaching the center &# 34 ; is displayed . thereafter , the data terminal 1 reaches the communication line to the modem 72 , and when the cpu 11 is connected with the cpu 91 of the center , a message , &# 34 ; the machine is on line with the center &# 34 ; is displayed . the data terminal 1 receives data about the estimated time of having a serviceman , etc . from the center , and a message , &# 34 ; a service man will arrive at **:**&# 34 ; is displayed . after managing the trouble , the serviceman turns on the trouble reset switch 45 (&# 34 ; yes &# 34 ; at step s49 ), and thereby , a trouble reset signal is sentto the cpu 11 at step s50 . the cpu 11 receives the trouble reset signal andtransmits a message to the center that the machine has recovered . after thereset of trouble , the message block 400x of the display panel 40 becomes back in the usual state . the cpu 11 of the data terminal 1 carries out processing shown by flowcharts of fig6 through 9 , 11 and 12 . if the dip switch dip . sw4 is on at a time of turning on the copying machine4 , which requests initialization (&# 34 ; yes &# 34 ; at step s11 ), initialization is carried out at step s12 . the processing at the initialization step s12 , asshown in fig1 , depends on the on / off states of the dip switches dip . sw1 , dip . sw2 and dip . sw3 . for example , when the copying machine 4 is turned on while the dip switchesdip . sw1 , dip . sw2 and dip . sw3 are off , off and on respectively , it requests input of the id of the data terminal 1 . a number is input by use of the ten - key 40b , and the print key 40a is pressed . thereby , the input number is stored in the sram 15 as the id of the data terminal . thereafter , the copying machine 4 is turned off once . however , since the sram 15 has a backup battery , the sram 15 keeps the id of the data terminal . when the copying machine 4 is turned on while the dip switches dip . sw1 , dip . sw2 and dip . sw3 are off , on and off respectively , it requests input ofthe id of the center . a number is input by use of the ten - key 40b , and the print key 40a is pressed . thereby , the input number is stored in the sram 15 as the id of the center . thereafter , the copying machine 4 is turned off once . however , since the sram has a backup battery , the sram 15 keeps the id of the center . when the copying machine 4 is turned on while the dip switches dip . sw1 , dip . sw2 and dip . sw3 are off , on and on respectively , it requests input of the telephone number of the center . a number is input by use of the ten - key 40b , and the print key 40a is pressed . thereby , the input number is stored in the sram 15 as the telephone number of the center . thereafter , the copying machine 4 is turned off once . however , since the sram has a backup battery , the sram 15 keeps the telephone number of the center . in this way , the id of the data terminal , the id of the center and the telephone number of the center are stored in the sram 15 . when the copying machine 4 is turned on while the dip switches dip . sw1 , dip . sw2 and dip . sw3 are all on , it requests selection of communication mode . this is to select the mode of communication with the center when thecommunication is not significant and not necessary . more specifically , in carrying out periodic communication , when only a small number of copies have been made since the previous periodic communication , the communication is not necessary . in carrying out copy number communication , when it is only a short time since the previous copy number communication , the communication is not necessary . there are mode 1 , mode 2 and mode 3 asoptions for the former case , and there are mode 4 , mode 5 and mode 6 as options for the latter case . the selections from these modes are made as follows . first , one of the numbers 1 , 2 and 3 is input by use of the ten - key 40b , and continuously one of the numbers 4 , 5 and 6 is input by use of the ten - key 40b . then , the print key 40a is pressed , and thereby , the input numbers are stored in the sram 15 as the modes of communication in the above - described cases . for example , by inputting 2 and 4 by use of the ten - key 40b and pressing the print key 40a thereafter , the mode 2 and the mode 6 are selected and stored in the sram 15 . then , the copying machine 4is turned off once . however , since the sram 15 has a battery backup , the sram 15 keeps the selected data transmission modes . if the dip switch dip . sw4 is off at a time of turning on the copying machine 4 (&# 34 ; no &# 34 ; at step s11 ), the processing is carried out following steps s13 through s22 . every time a processed sheet is ejected from the copying machine 4 , count data are transmitted to the cpu 11 and are stored in the sram 15 at step s13 , and element data are transmitted and stored in the sram 15 at step s14 . at step s15 , element data of each item are processed to calculate theaverage and the variance , and the average and the variance are stored in the sram 15 . when data are not transmitted from the copying machine 4 within a specified time after ejection of a sheet , it is checked at step s16 whether a trouble code is transmitted from the cpu 41 to determine whether trouble communication should be carried out . step s17 is a step of determining whether periodic communication should be carried out . more specifically , the present time of the clock 17 is compared with the time of next periodic communication stored in the sram 15 . step s18 is a step of determining whether copy number communication should be carried out . more specifically , the value of the total copy counter received at step s13 is compared with the copy number stored in the sram 15 . step s19 is a step of determining whether alarming communication should be carried out . more specifically , it is checked whether the addition of the average and the variance of each item of element data is over a threshold value stored in the sram 15 . step s20 is a step of determining whether manual communication should be carried out . it is checked whether the push switch 21 is pressed . step s21 is a step ofdetermining whether pm communication should be carried out . it is checked whether , after an exchange of parts , the corresponding pm counter is reset . when communication with the center is requested at any one of the steps s16through s21 , communication is carried out at step s22 . first , the modem 52 is actuated to call up the modem 72 of the center , and the modem 52 transmits the id of the center . when the id is correct , the id of the dataterminal is transmitted to the center , and then , exchange of information iscarried out following the procedure shown by fig7 . if the modem 52 cannotreach the communication line of the center within a specified period , if the id of the center is incorrect , or if the data terminal does not receive data from the center within a specified time after completion of sending data , an error message is displayed in the message block 400x of the operation panel 40 . when trouble communication is to be carried out (&# 34 ; yes &# 34 ; at step s71 ), at step s71a , a trouble code which indicates the kind of the trouble is transmitted to the center , and service data , such as the estimated time ofhaving a serviceman , are sent from the center . when alarming communication is to be carried out (&# 34 ; yes &# 34 ; at step s72 ), alarming data which indicate thenecessity of maintenance of any part are transmitted to the center at step s72a . when pm communication is to be carried out (&# 34 ; yes &# 34 ; at step s73 ), pm data which indicate the completion of an exchange of parts are transmittedto the center at step s73a . when periodic communication is to be carried out (&# 34 ; yes &# 34 ; at step s74 ), countdata and element data are transmitted in a first mode at step s74a following a procedure shown by fig8 . the current value of the total copycounter is compared with the value of the same counter at the previous periodic communication , and if the difference between the values is over 100 (&# 34 ; yes &# 34 ; at step s81 ), items of count data and element data which have changed since the previous periodic communication are transmitted to the center at step s85 . if the difference between the values of the total copy counter is not more than 100 (&# 34 ; no &# 34 ; at step s81 ), the communication is carried out according tothe mode selected by use of the dip switches . for example , if mode 1 is selected , the communication is canceled at step s83 . if mode 2 is selected , a status which indicates that a small number of copies have beenmade since the previous periodic communication is sent at step s84 . if mode3 is selected , count data and element data are transmitted to the center atstep s85 in the same manner as the case wherein the difference between the counter values is over 100 . further , as a possible modification of mode 1 , in the next communication ( for example , alarming communication ) after the cancellation at step s83 , a status which indicates that the previous periodic communication was canceled is sent . the judgment at step s81 is possible because the sram 15 has a data renewing area a1 and a transmitted data storing area a2 ( see fig1 ). thedata renewing area a1 has the latest data sent from the copying machine 4 , and the transmitted data storing area a2 keeps data which were transmittedto the center in the previous periodic communication . at the time of data transmission to the center , data are transferred from the data renewing area a1 to the transmitted data storing area a2 as indicated by x in fig1 . the judgment at step s81 is made by comparing data in these two areas . the element data stored in the areas a1 and a2 are the average and varianceof each item . at step s85 , the count data a11 in the data renewing area a1 are compared with the count data a21 in the transmitted data storing area a2 , and the element data a12 in the data renewing area a1 are compared with the element data a22 in the transmitted data storing area a2 . further , it is possible to control the communication in accordance with the comparison result at step s85 . for example , when the data a11 and a12 in the renewing area a1 are equal or so similar as to be regarded equal tothe data a21 and a22 in the transmitted data storing area a2 , the communication is canceled . in this case , it is possible to send information that the count data and the element data are very similar to those transmitted in the previous periodic communication . the count data stored in the sram 15 , as shown in fig1 , mean the value of the total copy counter , the value of the copy counter by size , the value of the jam counter by portion , the value of the trouble counter by portion and the value of the pm counter by part . the element data stored in the sram 15 mean the sheet traveling time , the surface potential of thephotosensitive drum , the toner density of the developer , the developing bias voltage , the amount of toner stuck on the photosensitive drum and thegrid voltage of the charger . the total volume of the count data and the element data are approximately 2 kilobytes . in order to transmit all the count data and the element data to the center , it takes approximately 15 seconds at a speed of 1200 bits per second . however , since only the data which have changed since the previous communication are transmitted at step s85 , the data transmission time can be shortened to about 1 / 10 on average . additionally , the sram 15 is stored with data which are sent from the center during communication with the center , such as the date and time of next periodic communication , the copy number designating the next copy number communication , threshold values which are references to determine the necessity of alarming communication , etc . after transmitting the count data and the element data to the center in thefirst mode as described above at step s74a , the cpu 11 receives data from the center at step s74b . if the difference between the values of the totalcopy counter is over 100 (&# 34 ; yes &# 34 ; at step s81 ), after sending the count data and element data at step s85 , the cpu 11 receives data from the center following the procedure shown by fig1 . more specifically , the cpu 11 receives the date and time of next periodic communication at step s112 andreceives threshold values of the items of element data which have changed since the previous periodic communication at step s113 , and these receiveddata are stored in the sram 15 . even if the difference between the values of the total copy counter is not more than 100 (&# 34 ; no &# 34 ; at step s81 ), when mode 2 or mode 3 is selected (&# 34 ; yes &# 34 ; at step s111 ), the cpu receives data from the center in the same manner . however , when mode 1 is selected , the cpu 11 does not communicate with the center , and the date and time of nextperiodic communication is calculated from the data stored in the sram 15 atstep s114 . for example , the date and time of next periodic communication isset to be seven days after . this is a longer period than the reference period at step s91 ( see fig9 ) in a second mode of count data / element data transmission , which will be described later . when copy number communication is to be carried out (&# 34 ; yes &# 34 ; at step s75 ), count data and element data are transmitted to the center at step s75a in the second mode shown by fig9 . the present time indicated by the clock 17 is compared with the time stored in the sram 15 as the time of previouscopy number communication , and if the difference is over 24 hours (&# 34 ; yes &# 34 ; atstep s91 ), items of count data and element data which have changed since the previous copy number communication are transmitted at step s95 . if the difference is not more than 24 hours (&# 34 ; no &# 34 ; at step s91 ), the communication is carried out according to the mode selected by use of the dip switches . for example , if mode 4 is selected , the communication is canceled at step s93 . if mode 5 is selected , a status which indicates thatit is a short time since the previous copy number communication is transmitted at step s94 . if mode 6 is selected , count data and element data are transmitted at step s95 in the same manner as the case wherein the difference is over 24 hours . further , as a possible modification of mode 4 , in the next communication ( for example , alarming communication ) after the cancellation at step s83 , a status which indicates that the previous copy number communication was canceled is sent . it is also possible to , when the count data and the element data are judged at step s95 to be very similar to those transmitted in the previous copy number data transmission , send such information to the center . after transmitting the count data and the element data to the center in thesecond mode as described above at step s75a , the cpu 11 receives data from the center at step s75b . if the time difference is over 24 hours (&# 34 ; yes &# 34 ; atstep s91 ), after sending the count data and element data at step s95 , the cpu receives data from the center following the procedure shown by fig1 . more specifically , the cpu 11 receives the copy number at which the next copy number communication is to be carried out at step s122 and receives threshold values of the items of element data which have changed since the previous copy number communication at step s123 , and these received data are stored in the sram 15 . even if the time difference is not more than 24 hours (&# 34 ; no &# 34 ; at step s91 ), when mode 5 or mode 6 is selected (&# 34 ; yes &# 34 ; at step s122 ), the cpu 11 receives data from the center inthe same manner . however , when mode 4 is selected , the cpu 11 does not communicate with the center , and the copy number at which the next copy number communication is to be carried out is calculated from the data stored in the sram 15 at step s114 . for example , the copy number is set tobe 1000 . this is a larger number than the reference number at step s81 ( seefig8 ) in the first mode of count data / element data transmission . in manual communication (&# 34 ; yes &# 34 ; at step s76 ), all the count data and elementdata in the sram 15 are transmitted to the center at step s76a , whereas in regular communication ( periodic communication and copy number communication ), only items of count data and element data which have changed since the previous regular communication are transmitted ( see steps85 of fig8 and step s95 of fig9 ). in other words , all the data can betransmitted to the center by conducting manual communication . although the present invention has been described in connection with the preferred embodiment , it is to be noted that various changes and modifications are possible to those who are skilled in the art . such changes and modifications are to be understood as being within the scope of the present invention .