GB2075721A - Apparatus for determining sheet sizes - Google Patents

Abstract

Apparatus for determining the size of a sheet having one of a plurality of determined sizes has a number of sensors less than the number of sheet widths, which sensors are arranged across the sheet location. From the length and width information determined by the sensors the size of the sheet can be identified using a catalogue of sheet sizes stored in a microprocessor memory. The microprocessor may then be used to control operations which are area dependent in a processing station or stations. One application is in the electrolytic removal of silver from a fixer bath in the processing of X-Ray films. Identification of the sheet sizes enables reliable estimation of the silver salts dissolved in the fixer from the films. This enables the electrolysis to be controlled so as to maintain the concentration of silver salts in the fixer at a suitable low level.

Description

SPECIFICATION Sheet processing The present invention relates to identification of sheet sizes and more particularly for such identification for the processing of sheet materials of different predetermined sizes within a predetermined range. The processing may be photographic processing, and may result in the dissolving of silver, in the form of silver salts, in a processing liquid, the amount of silver being related to the size of the processed sheets. A particular aspect of the invention is concerned with such identification for controlling the recovery of such silver from the processing liquid by means of an electrolytic cell.

According ta the present invention there is provided apparatus for determining the size of a sheet having one of a plurality of determined sizes, comprising a number of sheet sensors arranged across a sheet location, the number of sensors being less than the number of sheet widths so that a predetermined number of sensors are actuated by a sheet of a predetermined size, means for measuring the length of a sheet and for producing an output corresponding to the length, and a micro-processor having stored therein the parameters of said predetermined sizes, and the numbers of sensors actuated by a sheet of each predetermined size and the output corresponding to the length thereof, whereby the microprocessor produces a signal corresponding to the size of the sheet.

The present invention will be described with reference to its use in the control of an electrolytic cell, which use is additionally described and claimed, in Patent Application No. 7932605 (Serial No. 2033612), by way of example, with reference to the accompanying drawings in which: Figure 1 shows an electrolytic cell connected to a photographic fixer bath for use with the present invention; Figure 2 is a graph showing the relationship between electrolysis time and silver content of a typical fixer bath; Figures 3-3d show a flow chart for a control system employing the present invention.

In Figure 1 is shown a photographic processor fixer tank 10 connected for mixing circulation of the fixer through a path including an electrolytic cell 12, for electrolysing dissolved silver from the fixer. A fixer circulation path extends from the tank 10, to a fixer circulation pump 14, a filter 18 and hence returns to the tank 10. During normal operation of the processor, the pump 14 runs continuously to prevent stagnation and local depletion of the fixer.

A flow tapping connector 16 in the above described path provides a secondary path extending through an electrolysis circulation pump 20 and the electrolytic cell 12, returning to the above path again at the flow tapping connector 16.

A suitable electrolytic cell 12, is disclosed in U.K. Patent Application No. 51022/76 (Serial No. ) and Research Disclosure, Item 16950. May 1978.

The pump 20 operates to divert the circulating fixer through the electrolytic cell 16. The application of electrolysing current to the electrolytic cell 12 is controlled by a control unit 22.

In Figure 2 the concentration of dissolved silver salts, expressed in terms of pure silver, is plotted against elapsed time when an electrolysing current of 10 amps is passed through the cell 12. The capacity of the system is typically 20 litres of fixer, and hence the vertical axis of the graph is scaled both in grams of silver/litre of fixer and total silver dissolved in the fixer, in grams.

As the concentration of silver in the fixer decreases from the initial concentration of 2.5 grams/litre (50 grams total silver), there is a fall in the efficiency of electrolysis, that is the ratio of the silver deposited per coulomb to the electro-chemical equivalent of silver decreases. This is due to the lower concentration of silver in the fixer and the increased inhibiting effect of the other components of the fixer. Thus a curve of the shape shown in Figure 2 is produced.

There are a number of advantages from maintaining a low concentration of silver in the fixer bath. The tendency to form polynuclear silver complexes is reduced and the washing of film sheets is made easier. The amount of silver in fixer carried over to the wash water in the next processing bath by the film sheets is reduced. When replenishment or replacement of the fixer is necessary the amount of silver in any waste fixer is reduced making it easier to comply with pollution standards.

Maintaining too low a concentration of silver in the fixer presents its own problems where electrolysis is concerned, in that if electrolysis is continued at low silver concentrations then other reactions than the deposition of silver take place. For example, in a typical thiosulphate fixer, silver sulphide and hydrogen sulphide could be produced, the first of which causes damage to the fixer, and the second, if released into the atmosphere, produces unsatisfactory working conditions.

However, as will be seen from Figure 2, when the concentration of silver has fallen to 0.2 grams/litre of fixer the rate of electrolysis has fallen to a low level (approximately 2% efficient) and a small error in the assessment of the time required for electrolysis at this level produces a very low risk of over-electrolysis.

A satisfactory approximation to the curve shown in Figure 2 can be obtained by a series of straight lines, such as AB, BC, CD, DE and EF. The line EF represents a concentration of silver of between 0.1 and 0.2 grams/litre, which is the concentration range which is preferably as giving a low silver content without incurring the risk of decomposing the developer.

Direct coupling of an electrolytic cell to the fixing bath is known in larger photographic processing plant, for example in motion picture processing, where skilled staff are available to monitor the silver content of the fixer and so adequate control of the electrolysis can be provided. In small processing stations, for example in the radiography departments of hospitals, where normally staff are not available to provide the necessary control, such an arrangement has not been common.

The amount of silver added to the fixing bath 12 by processing can be computed from the area of material processed and from a factor which is an average of the rate of dissolving of silver from a range of material sizes.

It is known to determine the area of a sheet of photographic material passed into a processor by using sensors, such as photo sensors to determine both the width and length of the sheet, disclosed in U.K. Patent Specification No. 1,213,941. It is also possible to use such sensors to measure the density of the image on the photographic material and hence provide a basis for computation of the silver dissolved in the fixing bath.

The use of the invention is based on the appreciation that a limited number of sheet sizes are normally used in any particular location, and in fact, the total number of medical X-ray sheet film sizes catalogued is abouttwenty.

If an accurate measurement of the length ofa sheet is made, then by storing in a microprocessor/memory system the lengths and widths of sheets, it is possible to identify the full range of sheet sizes using a limited number of sheet sensors arranged across the width of the sheet, the number of sensors being less then the number of sheet widths. Subsequently, for simplicity, the microprocessor/memory system will be referred to as a microprocessor. In the preferred embodiment of the invention sheets are fed into the processor at one inch per second (25 mm/sec), and the length sensing mechanism is interrogated by the microprocessor at a clock frequency of 110 Hz. Thus the length is measured in increments of 10 in. = 0.009 in. or 0.23 mm.

There are five optoelectronic sheet sensors 208, 210, 212, 214, 216 (See Figure 3a) arranged across the sheet feed path, together with a microswitch 206 which is operated on the movement of a sheet into the feed path.

In a typical X-ray installation, it is usual for a particular size of film sheet to be used for a particular application. Hence, for any given sheet size, the density of the image is predictable, and hence the amount of silver which will be removed therefrom by the fixing bath is predictable also. Thus, identifying a sheet size enables a reasonable assessment of the silver added to the fixer solution to be made, and this information can be stored in the microprocessor as well. Moreover, this information can be modified to suit the particular characteristics of an individual installation.

In addition, use may be made of non-standard sheet sizes, such as may be made by cutting standard sheets, and a factor introduced in the microprocessor operation to cover these on a group basis. Also, in many applications, rolls of film are used, and it is possible to recognise these by their length, and to introduce a factor for silver added to the fixer bath computed on the basis of silver from unit length of film of a given width multiplied by the length of film processed.

Hence, it is possible to establish the operating point on the graph of Figure 2, which operating point is continuaily up-dated, and thus to determine the time for which the fixed electrolysis current of 10 amps in the electrolytic cell 12 must be applied to reach the region EF of the graph.

Two additional features may be included in the control of the electrolysis. Firstly, when no electrolysis current is applied, the silver tends to redissolve in the fixer from the electrode, and this requires compensation. Secondly, when a new electrode is fitted to the electrolytic cell, to ensure satisfactory bonding of the silver to it the current should start at a low level (typically 3 amps) until a certain quantity qf silver has been deposited on the electrode, after which the current may be increased to normal.

The microprocessor in the control unit 22 may be used to store information regarding the operation of the processor and the electrolytic cell, such as: (i) Number of sheets of each size of film processed; (ii) Quantity of silver dissolved from the sheets of film into processing solution.

(iii) Quantity of silver electrolysed from solution; (iv) Time elapsed since previous use of processor.

This information can be read from the microprocessor into a teleprinter or other output unit. The ability to interface with a teleprinter is the reason for the choice of a clock frequency of 110 Hz, referred to above.

In Figure 3 is shown the basic microprocessor flow chart, certain of the blocks being shown in greater detail in Figures 3a to 3d.

The cycle commences at START(102), followed by INITIALISE(104), which establishes the preliminary conditions for the microprocessor unit (MPU). SENDMPUOK(106) inhibits the system alarm for one second while the MPU is checked. If the MPU is found to have failed, then the alarm will sound after the one second inhibit has terminated. The next step is TTYPRINTOUTREQUEST? (108), when the inputs are examined to determine whether a teleprinter or other output device is connected to the MPU, and a printout of the stored information is being requested. If the answer is YES then SEND DATA TO TTY(1 10) follows, and the stored information is sent to the teleprinter or other output device via a subroutine before returning to the main loop. If the answer is NO, then the main loop is followed, in either case arriving at FILMINSERTED? (112). If the answer is YES then the path follows a subroutine to DECREMENT COUNTER (114) and DETERMINE FILM SIZE(1 16). The counterwhich is decremented counts in seconds, minutes, hours and days when the film processor is not in use, the counter being decremented by one hour for every film inserted in the processor as long as the counter holds a count greaterthan zero. As described later, if the counter reaches fourteen days the current is disabled and the fixer must be replaced.

The block DETERMINE FILM SIZE (116) is shown in greater detail in Figure 3a. The first two operations are MEASURE WIDTH (202) and MEASURE LENGTH (204). The film is fed into the processor and operates at least the microswitch 206, and possibly one or more of the optoelectronic sensors 208, 21, 212, 214, and 216.

The number of optoelectronic-sensors operated serves to establish that the width of the inserted film is within a particular one of five width groups, and thus the MEASURE WIDTH (202) function is carried out.

As described above the film is fed into the processor by means of rollers (not shown) at a speed of 1 inch per second (25 millimetres per second) and the time for the film to pass the microswitch 206 is measured in units of 1/110 second. This provides a measurement of the length of the film in units of 0.009 inches (0.23 millimetres).

If only the microswitch 206 is operated by the insertion of a film into the processor, then the answer to WIDTH < 20CM? (218) is YES. Subsequently, the questions and the sheet sizes corresponding to an answer of YES in each case are: LENGTHca 10CM7(220) - 10cm x 10cm (222) LENGTHca 18CM7 (224) - 13 cm x 18 cm (226) LENGTHca24CM7(228) - 18cm x24cm (230) LENGTHca30CM?(232)- 15cm x 30cm (234) LENGTH ca 40CM? (236) - 15 cm x 40 cm (238) LENGTHca43CMP(240) - 18cm x 43cm (242) If the answer to the first question is NO, then the flow chart proceeds to the second question and so on in succession.Thus the flow chart identifies a film as having, in this case, a width of less than 20 cm and a particular length of 10 cm, cm,24 cm,30 30cm, cm, or 43 cm.

The combinations of length and width selected are such that of the catalogued film sizes only one size will meet the particular length/width criteria, e.g. only a 18 cmx 24 cm film has a width of less than 20 cm and a length of 24 cm.

Where the width is less than 20 cm but the length is not such as to produce a YES answer to any of the questions regarding length, then the film is of a non-catalogue size and will be classified as SIZE OTHER-'A' (244), i.e. a size having a width of less than 20 cm but a non-catalogue length. Such a size will be either a cataiogue size which has been cut to give a smaller size, or a length cut from a roll. Such sizes can be grouped together and an average of the areas allowed for in the programme. Generally in a particular installation the incidence of such sizes will be low and the effects of differences between the 'calculated' and 'allowed for' average areas will produce an insignificant error in the programme.Where there is evidence that this is not so, the weighting given to such sizes can be adjusted or where the usage of a particular non-standard size at a particular location is significant, that size can be entered in the programme catalogue.

Additionally the 'other' area can be weighted in proportion to, or in some other relationship to, the length measured, e.g., if it is known that all non-catalogue lengths over a certain length are cut from a roll the area can be calculated readily.

If the film is of a width of 20 cm or greater, but less than 24cm, then the answer to WIDTH < 2OCM? (218) is NO, and the answer to WIDTH < 24CM? (246) is YES, the microswitch 206 and the optoelectronic sensor 208 being operated. In a similar manner to that already described, using blocks 248-256 film sizes 20 cm x 25 cm, 20 cm x 40 cm and SIZE OTHER 'B'can be identified. Further using blocks 258-286, sizes 24 cm x 30 cm, 30 cm x 30 cm, cm x 35cm, cm x 35 cm and SIZE OTHER 'C' SIZE OTHER 'D', and SIZE OTHER,' can be identified, the last three being non-catalogue sizes 24-30 cm wide, 30-35cm wide, and 25-40 cm wide, respectively.

If the width is 40 cm or greater and the answer to LENGTH ca 30CM7 (288) is YES then the size is 30 cm x 40 cm (290), while if the answer is NO but the answer to LENGTH ca 35CM (292) is YES, then the size is 35 cm x 43 cm (294). Finally, if the width is 40 cm or greater, but the length is neither 30 cm nor 35 cm, the film size is classified as SIZE OTHER 'F' (296).

Thus the size of the film inserted in the processor has been determined, and this size is then applied to the input of CALCULA TEAREA X SILVER FACTOR (298). From the stored information in the MPUwhich was referred to earlier, the amount of silver dissolved in the fixer can be determined, and when this amount is applied to INCREASE SILVER TOTAL (300) the information as to the amount of silver dissolved in the fixer is increased appropriately.The path then proceeds via BEEP (302), which causes a short alarm of a fraction of a second to be sounded to indicate that a further film may be inserted, to FAULT DETECTION (118), which is also arrived at directly if the answer to FILM INSERTED? (112) is NO FA UL T DETECTION (118) is shown in greater detail in Figure 3b. The fault detection operations are not all included in this block, as some are carried out more conveniently at other stages in the programme.

ANO answer to FILM INSERTED? (112) or an output from BEEP (302) produces an input to FAULT DETECTION (118) and in particular FILM SENSORS WORK? (402). If the answer is NO then the action is LIGHT 'SENSOR FAILED'LAMP (404) and an output is provided to TOTAL SILVER > 3071G? (408), but, if the answer is YES then the action is CANCEL 'SENSOR FAILED'LAMPIF ON (406). The cancellation of the 'sensor failed' condition is necessary to cover the situation of a momentary fault, e.g. where a loose piece of film or paper obscures a sensor and is then removed. The output is again to TOTAL SILYER > 3071G? (408).

3071 grams of silver is the weight of silver deposited on the electrode in the particular electrolytic cell 12 which gives a safe upper size limit for the plated electrode. While immediate electrode replacement is not essential, it should be carried out soon after this weight of silver is deposited, and though a warning is given, the electrolysis is not inhibited.

If the answer to TOTAL SILVER > 3071G? (408) is YES then the next step is LIGHT 'ELECTRODE'LAMP (410).

The subsequent step in this case and if the answer was NO, is to provide an output to 14 DAYS WITHOUT USE? (412). If the answer is YES the fixer is stale and needs replacement and an input is provided to DISABLE CURRENT (414) and thence to LIGHT'DISUSE'LAMP(416) whereby firstly the electrolysis current is removed and secondly the 'DISUSE' warning is illuminated. An input is now provided from LIGHT 'DISUSE' LAMP (416) to FILM INSERTED? (418), where if the answer is NO, a closed loop exists from the output to input of FILM INSERTED? (418) and the MPU becomes locked in this loop.If a film is inserted so that the answer becomes YES, then the MPU escapes from the closed loop and provides an input to START (102) and as DECREMENT COUNTER(114) will then be initiated as described above, one hours operation will be available before the lock-out occurs again, and emergency use of the processor is possible, though quality of the results may be suspect and the operator has been warned that the fixer should be changed as soon as possible.

If the answer to 14 DAYS WITHOUT USE? (412) is NO then an output is provided to IS REPLENISHMENT COUNTER = 50? (120). The replenishment counter is incremented for each 0.01 gram of silver electrolysed, and when the count reaches a preset number, in this embodiment fifty, a YES output is provided to ZERO COUNTER (122) which resets the replenishment counter to zero and subsequently to START PUMP TIMER (124). The replenishment pump is then run for a predetermined time which is sufficient to replace the fixer lost by carry over on the films and liquid loss by evaporation and to provide an excess which causes an amount of used fixer to overflow to waste. Subsequently or by a NO answer to IS REPLENISHMENT COUNTER = 50? (120) an input is provided to ELECTROLYSIS CONTROL (126) which is shown in greater detail in Figures 3c and 3d.

The first steps carried out in the control of the electrolysis are MEASURE CURRENT (450), MEASURE VOLTAGE (452) and MEASUREFACTOR (454). The first two steps refer to measurement of the current through the cell 12, and the voltage applied across the cell 12. The MEASUREFACTOR (454) step refers to the 'silver factor' representative of the silver salts dissolved in the fixer solution.

The programme then proceeds to SILVER IN SOLUTION > 3.99G? (456). As will be seen from Figure 2 a quantity of 3.99 grams of silver dissolved in the fixer corresponds to point Eon the graph. A smaller quantity of silver then 3.99 grams meant that electrolysis is not required, and a NO answer means that the MPU shou Id DISABLE CURRENTIPUMP (490), followed by HAS 1 SECOND ELAPSED? (492). If the answer is NO then the question is repeated until one second has elapsed and the answer then becomes YES and the next step is INCREMENT COUNTER (494) where the timing counter is incremented to record time out of use.

The next group of blocks 496,498, 500, 502, 504 apply the electrolysing current to compensate for the redissolving of silver from the anode of the electrolytic cell 12, by passing a burst of current through the cell 12 every hour when the cell 12 is not in use. To achieve this the first block is HAS 1 HOUR ELAPSED? (496) if the answer is NO, then the remainder of the blocks 498,500,502, 504 are by-passed. If the answer is YES, then the next question is TOTAL SILVER > 2047G? (498), to which a YES answer causes the application of a current of lOAMPS for 48 SECS (500), and a NO answer leads to the question TOTAL SIL VER > 255G? (502).

This causes the application of a current of lOAMPS for 24 SECS (504) for a YES answer, and no application of current for a NO answer. The application if current to compensate for the redissolving of silver is thus divided into three sectors, ten amps for forty-eight seconds for an anode having more than 2047 grams of silver deposited on it; ten amps for twenty-four seconds for an anode having between 255 and 2047 grams of silver deposited on it; and no current for an anode having less than 255 grams of silver deposited on it. Thus, the heavier and larger the anode, the greater the surface area of silver is exposed to the fixer on the anode, and the more current is applied.

If the answer to SILVERINSOLUTION > 3.99G? (456) is YES then subsequently TOTAL SILVER 75G7 (458) if the answer to this is NO then the current is limited to an application of 3 amps lasting ten seconds to ensure that the first 5 grams of silver deposited on the anode are deposited slowly to ensure good adhesion. The sequence is then ENABLE CURRENTIPUMP (406) and apply 3AMP CONTROL VOLTAGE (462). Then the current is checked by the sequence CURRENT TOO HIGH? (464), YES resulting in DECREASE VOLTAGE (470), NO leading to CURRENT TOO LOW? (466), YES resulting in INCREASE VOLTAGE, and NO leading to 10 SECONDS ELAPSED? (468). If the ten second period has not elapsed, then NO leads to PUMP WORKING? (474), which may be reached also from DECREASE VOLTAGE (470) or INCREASE VOLTAGE (472).An answer YES from PUMP WORKING? (474) then leads to VOLTAGE TOO HIGH? (480). The voltage referred to is the voltage across the cell, and if it exceeds a preset limit, then the cell is open-circuit. If the answer is NO, then the loop is completed to 3AMP CONTROL VOLTAGE(462), while YES provides an input to LIGHT 'CELL' LAMP (482) and thence to SOUND ALARM (478). An answer NO from PUMP WORKING? (474) provides an input to LIGHT 'PUMP'LAMP (476) and thence again to SOUND ALARM (478). From SOUNDALARM (478) the input is to START (102).

If the ten seconds has elapsed then YES leads to INCREMENTREPLENISH COUNTER (484), INCREASE TOTAL SILVER B Y0.01G (486) and DECREASE SILVER IN SOLUTION B Y0.01G (488). As a result the replenishment counter is incremented, the stored record of the silver deposited on the anode is increased by 0.01 gram, and the stored record of the amount of silver dissolved in the fixer is reduced by 0.01 gram.

If the answer to TOTAL SIL VER > 5G? (458) is YES, then the input is to blocks 506, 508, 510, 512, 514, 516, 518 which simulate the graph shown in Figure 2. The first question is SILVER IN SOLUTION > 25G? (506) and YES means the cell 12 is operating in the portion AB of the graph of Figure 2, and requires ELECTROLYSIS TIME 1. 1 SECONDS (508). NO means the cell is operating below B on the graph, and leads to SILVER IN SOLUTION > 15G? (510), which is the cell is operating in the region BC provides a YES answer and a longer ELECTROLYSIS TIME 1.8 SECONDS (512). NO means the cell 12 is operating below C on the graph, and YES to SILVER IN SOLUTION > BG? (514) then means the cell 12 is operating in the region CD on the graph giving ELECTROLYSIS TIME2.4 SECONDS (516).NO to SILVER IN SOLUTION > 8G? (514) means that the cell 12 is operating in the region DE of the graph of Figure 2, as from SILVER IN SOLUTION > 3.99G? (456) it is already known that area of operation of the cell 12 is above E, and ELECTROLYSIS TIME 4.7 SECONDS (518).

From the appropriate ELECTROLYSIS TIME block 508,512,516,518 there is an input to ENABLE CURRENTIPUMP (520), and thence to 10AMPCONTROL VOLTAGE (522). Next the question is CURRENT TOO HIGH? (524) for which a YES answer leads to DECREASE CONTROL VOLTAGE(526), and a NO answer to CURRENT TOO LOW? (528). A YES answer to this question in INCREASE CONTROL VOLTAGE (530) and NO in TIME ELAPSED? (532) this the electrolysis time from 508, 512, 516 or 518. A NO answer, as well as outputs from DECREASE CONTROL VOLTAGE (526), and INCREASE CONTROL VOLTAGE(530) leas to PUMP WORKING? (540).A YES to this question leads to CONTROL VOLTAGE TOO HIGH? (544), to which NO gives CONTROL VOLTAGE TOO LOW? (548). A NO to this question closes the loop to 10 AMP CONTROL VOLTAGE (522). If the pump is not working, then the answer to PUMP WORKING? (540) is NO, and gives LIGHT'PUMP'LAMP(542) and SOUNDALARM (552). A YESto CONTROL VOLTAGE TOO HIGH? (544), or CONTROL VOLTAGE TOO LOW? (548) leads too LIGHT 'CELL'LAMP (546 and 550 respectively, and SOUND ALARM (552).

If the control voltage is too high, i.e. it passes a preset high limit, then the cell circuit is open circuit and a fault condition exists. Similarly, if the control voltage is too low, then a short circuit exists, for example the silver has bridged between the anode and cathode, and again a fault condition exists. SOUND ALARM (552) leads to START(102).

When the electrolysis time has been completed, the answer to TIME ELAPSED? (532) becomes YES, leading to INCREMENT REPLENISH COUNTER (534), INCREASE TOTAL SILVERBY0.01G (536) and DECREASE SILVER IN SOLUTION B Ya0 1G (538) which are similar to 484,486, 488 respectively described above.

Both DECREASE SILVER IN SOLUTION B Y 0.01G (488 and 538) lead to ZERO MEMOR YREOUEST? (128) on Figure 3. This result in a YES response for a 'fresh start' condition when the equipment is being commissioned or the fixer solution is drained and renewed due to 'disuse' for example. This results in CLEAR MEMORY (130). Following this step or a NO output from ZERO MEMOR YREOUEST? (128) the loop is closed by an input to SENDMPUOK(106).

The flow chart can be modified obviously in many ways, in that various blocks and loops can be interchanged, and certain blocks carrying out the same basic function can be combined. The flow chart shown includes one specific embodiment of the size-determining apparatus of the present invention.

Where an installation is used in a hospital it is possible that the pattern of use is time dependent, for example one source of film sheets to be processed may be a particular clinic which operates on only one or two days a week, but whose output is sufficient to distort the normal distribution. Further, at nights and weekends, the chief source of film sheets for processing is the casualty department where the distribution will again be different.

It may therefore be advantageous in such a situation to adjust the proportionality factor on a time-dependent basis.

Claims (2)

1. Apparatus for determining the size of a sheet having one of a plurality of determined sizes, comprising a number of sheet sensors arranged across a sheet location, the number of sensors being less than the number of sheet widths so that a predetermined number of sensors are actuated by a sheet of a predetermined size, means for measuring the length of a sheet and for producing an output corresponding to the length, and a microprocessor having stored therein the parameters of said predetermined sizes, and the numbers of sensors actuated by a sheet of each predetermined size and the output corresponding to the length thereof, whereby the microprocessor produces a signal corresponding to the size of the sheet.

2. Apparatus determining the size of a sheet substantially as hereinbefore described with reference to and as illustrated in Figures 3 to 3d of the accompanying drawings.