referring to fig1 the system embodying the invention is shown in block form . it will be understood that the coin box / bill acceptor ( 3 ), card reader / encoder ( 4 ) and copier ( 2 ) are shown as examples of such devices , only , and do not actually represent any particular copier , etc . in fact , the invention is not limited to copiers , but is useful with any application in which it is desired to use an escrow controller with a vending machine in which the items vended must move along a vend path which is more than one article long . any device of the kinds described , chosen from among the many commercially available , can be used within the teachings of the invention , so long as it is capable of emitting , and responding to , the signals described in detail below . in fig1 the escrow credit controller is represented by box ( 1 ). in practical installations , this may well be incorporated into a single physical box with the coin acceptor , bill acceptor , change maker and possibly a card reader / encoder such as the vendacard ( r ) marketed by the assignee of this invention . the controller ( 1 ) will preferably have a readout ( 29 ) for communications with the customer . the readout will indicate the amount of money escrowed , and could also be programmed to produce messages such as &# 34 ; error &# 34 ; or &# 34 ; no change &# 34 ;, or the like , if the displays chosen are capable of such . the controller may also have a value - return button ( 30 ), the function of which is explained below , if the controller is not integrated with the coin or card mechanism . the controller has inputs for value accepted ( 32 ), value - return ( 33 ) and item - vended ( 34 ). it has outputs for enabling the vending machine ( 36 ) and returning remaining value in escrow ( 35 ). the actual nature of the signals received and emitted are not important , and will vary in a manner well - known to the art . for example , the &# 34 ; value in &# 34 ; signal from a coin acceptor is usually a serial train of pulses , each pulse representing a standard coin value ( i . e . a nickel is one pulse , a dime is two , a quarter is five , etc .). the same signal from a vendacard ( r ) reader might be a serial ascii - encoded number , or a parallel data line of &# 34 ; n &# 34 ; bits , or perhaps a simple train of pulses similar to the coin box application . similarly , the &# 34 ; value return &# 34 ; for a coin changer mechanism might be three lines , one each for nickels , dimes and quarters , each of which is pulsed to release a coin of the appropriate denomination , or might be a serial data stream giving a numeric coin value to be returned to a &# 34 ; smart &# 34 ; changer . for a card encoder , the same signal would be a serial data stream specifying the data to be re - encoded on the card . the &# 34 ; on / off &# 34 ; signals such as &# 34 ; enable &# 34 ;, &# 34 ; return &# 34 ; and &# 34 ; vended &# 34 ; could be active low , active high , pulses of various lengths , or any combination . all of these variations could be accomodated easily within the capability of one skilled in the art . the general operation of an escrow controller system is as follows : a customer inserts value into the system through a value accepting element , either by putting coins ( 21 ) or bills ( 22 ) in the coin / bill acceptor ( 23 ), or by inserting a magnetically - encoded card ( 28 ) such as used in the vendacard ( r ) system into an appropriate reader / encoder ( 4 ). if coins ( 21 ) are deposited , they may be sorted into tubes ( 24 ) in a changer ( 25 ) for later use in making change , or just dumped into a coin box . the value accepting element generates a &# 34 ; value added &# 34 ; signal ( 18 ), which is accumulated in the controller ( 1 ) and indicated on the display ( 29 ). in prior art controllers , as soon as the value accumulated exceeded a single vend price ( one copy , one can of soda , etc ) the controller turned on the &# 34 ; enable &# 34 ; line ( 16 ), which allowed the vending apparatus to accept a choice from the customer . in this example , the &# 34 ; print &# 34 ; button would become active on the copier , and the customer could then make a copy by pushing that button ( 31 ). the fact that a vend was made is indicated by the vending machine putting a signal on the &# 34 ; vended &# 34 ; line ( or &# 34 ; copy count &# 34 ;) ( 17 ). upon receipt of the signal , the value of the vend is subtracted from the escrow balance . in prior art controllers , when the escrow balance declines to less than one vend price , the enable line is turned off . the controller usually then issues a &# 34 ; value return &# 34 ; signal ( 20 ) to the coin changer ( 25 ) or card encoder ( 4 ), as appropriate , if there is any change due . the coin box ( 3 ) (&# 34 ; coin box &# 34 ; usually includes the coin and / or bill acceptor , and changer mechanism ), card reader / encoder ( 4 ) or controller ( 1 ) may have &# 34 ; coin return &# 34 ; switches ( 26 ), ( 27 ) and ( 30 ) respectively , which activate a &# 34 ; return switch &# 34 ; line ( 19 ). when the controller receives this signal , the enable line is turned off , and the remaining value is returned . the copier at ( 2 ) is shown in a schematic cut - away form to allow an understanding of the problem addressed by the invention . to make a copy , the paper in the copier ( 2 ) is picked up from an input tray ( 5 ) and is conveyed by rollers ( 8 ) to the drum ( 7 ). the toner image on the drum ( 7 ) is deposited on the paper , which is pulled along by the drum and rollers ( 9 ) past heater ( 10 ) and fuser rollers ( 11 ), which fuse the toner to the paper . the paper then is ejected into the copy hopper ( 6 ). three sheets of paper ( 13 , 14 and 15 ) are shown in the paper path in the drawing . paper ( 13 ) has just been picked up , unfused copy ( 14 ) is just leaving the drum , and finished copy ( 15 ) is leaving the machine for the hopper . in common with many copying machines , the example machine counts the copies with a switch ( 12 ) in the paper path just before the copy exits the machine . this switch generates the &# 34 ; vended &# 34 ; signal sent to the controller , and increments the internal copy counter . the placement of the switch ensures that a copy will not be counted until it actually is made , but it poses a problem which can be seen in the drawing . the paper path in the machine shown is ( at least ) three copies long . that is , allowing for registration of the drum , pick - up time , etc , up to three copies may be in process at any given time . in the example shown , the maximum number of copies are in the path . copy ( 15 ) has just been counted by switch ( 12 ), and the &# 34 ; vended &# 34 ; signal has been sent to the escrow controller the phase and two copies 13 and 14 are in the vend path yet to be counted as vended . as in all external copier controllers , the value of the copy is noted upon receipt of the vended signal from the copier . in an escrow controller , the value of the copy may then be subtracted from the remaining escrow balance . suppose , in the example , the customer had deposited ( or there remained ) an escrow balance sufficient to pay for a single copy ( but not enough for two ). when copy ( 15 ) passed switch ( 12 ) the balance would then be less than one copy in value . in prior art escrow controllers , the enable ( 16 ) line would then be disabled ( either immediately , or in accordance with the present inventor &# 39 ; s prior pate after a delay ). however , there are still two copies in the copy end path ( 13 , and 14 ). depending on the design of the copier , the customer will now get two free copies ( 13 , 14 ) and / or the machine will &# 34 ; catch &# 34 ; either ( 13 ) or ( 14 ) in the path and jam . either result is &# 34 ; undesirable &# 34 ; from the copier owner &# 39 ; s point of view . the latter situation is addressed in rademacher , et . al ., cited above . the present invention is designed to eliminate the former possibility . in the example of the copies in the vend path are copy ( 13 ) and copy ( 14 ). the method of operation of the invention is shown in detail in the flowcharts of fig2 a and 2b . the preferred method of implementing the method of the invention is through the use of a microcomputer , programmed in read - only - memory ( rom ) for the actual controller . the 68705 p - 3 microcomputer , manufactured by motorola , has been found to be suitable , although it will be understood by one skilled in the art that other microcomputer chips could be used as easily , or the invention could be constructed of discrete components , within the teachings of the invention . the method of interfacing the controller to the peripheral equipment ( coin box , copier , etc .) is conventional and well - known to the art . the following description relates the operation of the invention , as shown in the flowchart , and would be the same regardless of the actual hardware used to implement it . the controller is &# 34 ; initialized &# 34 ; ( label &# 34 ; start &# 34 ;) ( 40 ) by setting the escrow total ( total value deposited ) to zero , and displaying a message indicating readiness to begin . ( this could be as simple as a zero , or could be the word &# 34 ; ready &# 34 ;, or whatever seems appropriate which the display chosen can generate ). a trigger amount has been predetermined which is at least equal to one more than the number of units ( copies ) in the vend path ( copy path ). the &# 34 ; vend path &# 34 ; is defined as the value of the largest number of vend units which may be in motion through the vending machine simultaneously . the trigger amount may be chosen to be more than the value of one greater than the number of units in the vend path , if desired , but must not be less than the value of one more than the number of units in the vend path . a larger trigger amount might be chosen , for example , to discourage use of the escrow controller as a bill changer . the main operation loop begins at label &# 34 ; a &# 34 ; ( 41 ). the controller checks the value added inputs from the connected peripherals ( coin acceptor , bill acceptor , card reader ) ( 42 ). if there has been any value added ( 43 ) the value is added to the accumulated escrow total , and is shown in the display . the escrow total is compared with the trigger amount ( 46 ), as defined above . if the escrow total is larger than the trigger amount ( 47 ), then the &# 34 ; enable &# 34 ; line ( fig1 ( 16 )) is turned &# 34 ; on &# 34 ;, which allows the vending machine ( copier ) to accept orders from the customer . the controller then loops back to ( 41 ) to check for more value added . if there was no value added ( 44 ), the &# 34 ; vended &# 34 ; signal line ( 17 ) is checked to see if any units were vended ( copies made ) ( 44 ). if there have been copies made ( 45 ) the value of the units vended is subtracted from the escrow total , and the new total displayed . in some applications , it may be desired to use the controller in an &# 34 ; escrow - to - vend &# 34 ; mode , in which change is returned as soon as a vend is done , instead of waiting to see if the customer wants anything else , or if he wants to deposit more money . in such a case ( possibly after the delay ( 50 ) of rademacher , et . al ., the enable line is turned &# 34 ; off &# 34 ; ( 51 ), and the controller goes to the secondary loop ( label &# 34 ; b &# 34 ;- fig2 b , ( 57 )). normally , however , the controller will not be used in &# 34 ; escrow to vend &# 34 ; mode . accordingly , the controller next checks the escrow balance to see if it has dropped to a value which is less than or equal to the value of the number of units in the vend path ( 52 ). note that this value is at least one vend unit value less than the trigger amount . if it has , possibly after the cycle completion delay of rademacher , et . al . ( 53 ), the enable line is turned &# 34 ; off &# 34 ;( 54 ). the controller may optionally ( 55 ) be set to return change automatically when the escrow balance reaches a preselected point ( say , two vend unit values ). if this option is chosen , the controller checks the escrow value against this set point ( 56 ). if the escrow total is indeed below the limit ( 56 ), then the controller transfers to the secondary loop (&# 34 ; b &# 34 ; ( 57 )). if the automatic return option was not chosen , then the controller loops back ( 41 ) to check for value added , etc ., again . if there was no value added ( 42 ) and no vend signal ( 44 ), then the controller checks the &# 34 ; return &# 34 ; switch line to see if the customer has decided to get his remaining escrow balance back ( 48 ). if a return signal was received , the enable line is turned off ( 69 ) ( possibly after the delay of rademacher , et al ( 68 )) and the controller proceeds to the secondary loop (&# 34 ; b &# 34 ;( 57 )). this ends the discussion of the primary loop . the secondary loop comes into play when the controller has determined that the customer is done with vending , either because he has signalled this with the return signal or because the escrow balance has run out . the purpose of the secondary loop is to introduce a delay in returning any remaining escrow balance until all potential articles in the vend path have had an opportunity to clear . fig2 b shows the secondary loop , which is entered at label &# 34 ; b &# 34 ; ( 57 ). in order to avoid the use of the controller as a change maker , the secondary loop first checks to see if u any x units have been vended ( 58 ). if none have , and if the escrow total is greater than the trigger amount ( 59 ), and if the value was not added by card ( 60 ) then only the value in excess of the trigger amount is returned , and the controller returns to the primary loop . thus , the customer must make at least one copy before he can get his change ( less the cost of the copy ). obviously , if the value was added by card , no change is involved , and the value is simply returned ( 62 ). if at least one copy was made , then the controller begins a timed delay ( 63 ). the delay time is set to the length of time needed for the vend path to clear . on a copier , this may be 5 to 30 seconds , depending on the copier design . during the delay period , the controller checks for additional vend signals from vend units in the vend path as they clear the machine ( 65 ). if any vend signals are received during the delay ( 66 ), the value of the vends is subtracted from the escrow total and displayed , and the delay loop continues . after the delay time is over ( 64 ), the remaining value is returned ( 67 ), either with the coin changer or card encoder as appropriate , and the controller is re - initialized ( label &# 34 ; start &# 34 ; ( 40 )). accordingly , it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention . reference herein to details of the illustrated embodiments are not intended to limit the scope of the claims which themselves recite those features regarded as essential to the invention .