TECHNICAL FIELD

The present invention relates to processors of film a similar photosensitive media, in general; and, in particula to a method for the detection of invalid measured temperatu data in a system for controlling the temperature of chemica in such a processor.

BACKGROUND ART Photosensitive media processors, such as Kodak X-OM processors, are useful in applications like the automat processing of radiographic films for medical imaging purpose The processors automatically transport sheets or rolls photosensitive film, paper or the like (hereafter "film") fr a feed end of a film transport path, through a εeguence chemical processing tanks in which the film is develope fixed, and washed, and then through a dryer to a discharge receiving end. The processor typically has a fixed film pa length, so final image quality depends on factors includi the composition and temperature of the processing chemica (the processor "chemistry") , and the film transport spe (which determines the length of time the film is in conta with the chemistry) .

In a typical automatic processor of the type to which t invention relates, film transport speed is set at a consta rate and the chemistry is defined according to a pres recommended temperature, e.g. 94*F (34'C), with a specifi tolerance range of +/- X*. A temperature control system

- 2 - provided to keep the chemicals within the specified range.

Some processors use a thermowell located in a developer recirculation path to maintain a desired recommended developer chemical temperature. The thermowell has a cartridge heater inserted into one end of a hollow tubular body through which the developer is caused :to flow by means of a pump. A thermistor protruding into the thermowell flow path serves to monitor the recirculating developer temperature. The duty cycle of the heater is varied, based upon data received from the thermistor, as a function of the proximity of the measured actual temperature to a preestablished developer setpoint temperature. Until the setpoint temperature is reached, a "wait" light or similar annunciator signals the user that an undertemperature condition exists. Once the setpoint temperature is reached, heating and cooling cycles are initiated, as needed, in accordance with detected temperature variations from the setpoint. Cooling may be accomplished by operation of a solenoid valve which redirects the developer through a loop in the recirculation path which is in heat exchange relationship with cooler water in the wash tank. An overtemperature limit, typically 1/2° above setpoint temperature, is established as a reference to determine, proper operation of the heating control system. If an actual temperature greater than the overtemperature limit is sensed, an overtemperature error is signalled. The fixer, whose temperature is less critical, may have its own thermowell recirculation path or may be maintained at a temperature close to the developer temperature by directing it in heat exchange relationship with the developer. While processors used for radiographic image processing are traditionally configured to operate at a single film transport speed and developer setpoint temperature, new processors have been introduced which are εettable as to

transport speed and temperature, so the same processor can b used for multiple processing modes. A particular "mode i often referred to by a shorthand designation indicative of it associated "drop time," which corresponds to the- time laps from entry of the leading edge of a film at the feed end o the processor, until exit of the. trailing edge of the sam film at the discharge end. Kodak uses the designations "Kwik or "K/RA," "Rapid," "Standard," and "Extended" to refer t different user-selectable operating modes, each of which ha its own characteristic transport speed and developer setpoin temperature.

The operations and functions of automatic film processor are handled under control of electronic circuitry, includin a microprocessor connected to various process- sensors an subsidiary controls to receive and dispense electronic signal in accordance with predefined software program instructions Examples of such control circuitry are shown in U.S. Paten No. 4,300,828 and in U.S. patent application Serial No 07/494,647, the disclosures of both of which are incorporate herein by reference.

If film is run through a processor at system start-up o during a change of mode, before the chemistry temperature ha reached the designated setpoint setting for the selected mode the image development may well be of substandard quality and in worst case, not readable at all. For diagnostic imaging this may necessitate retake with consequential patien inconvenience and additional radiation exposure. In cases o radiographic imaging utilized for progress monitoring purpose during a surgical operating procedure, this may lead to othe undesirable consequences. It is, therefore, desirable to b able to prevent processing of exposed photosensitive medi until setpoint temperatures are reached. This may b accomplished by configuring the temperature control circuitr

to indicate a "ready" condition only when the developer, and optionally the fixer, chemicals reach their desired operating temperatures (i.e, until they are within X ^* of their setpoint temperatures). U.S. patent application Serial No.-.07/494,647 describes a system whereby the film drive transport mechanism is disabled to prevent the introduction of fresh film, until desired chemical temperatures are attained.

It is also desirable to be able to indicate a failure of the temperature control system. This is done conventionally by establishing an upper limit value, above which chemistry temperature would not normally be expected to go. This has the advantage of indicating an unacceptable overtemperature condition once setpoint temperature is reached, but provides no indication of improper operation prior to reaching setpoint. If the heat gain per unit time is too low, setpoint temperature may never be reached.

U.S. Patent application Serial No. , entitled "Method and Apparatus for Out-of-Rate Error Detection In a Film Processor," filed on even date herewith, describes a processor temperature control system in which malfunctions in operation of heating and cooling cycles are determined utilizing comparisons of actual and normal rates of change in chemical or dryer air temperature over time. Failures are indicated based on comparisons of time variations in measured actual temperatures for a given heating (or cooling) cycle, with expected variations for the same cycle assuming normal rates of heating (or cooling) under normal temperature control system operating conditions. If the actual rate of measured temperature increase (or decrease) deviates by more than a preeεtablished acceptable tolerance from the expected normal rate of increase (or decrease) , an error is indicated. The system can be set to shut down the processor _^ or disable the film drive transport mechanism (with user-controllable

- 5 - override) to prevent the introduction of fresh film,- if the error is not corrected. Such rate error detection scheme enables the rapid determination of temperature control system malfunction, prior to attainment of setpoint temperatures and flags errors which conventional error detection means would miss.

Regardless of the procedures employed for operational control or error diagnosis, processor temperature control systems suffer from the random occurrence of invalid actual temperature measurement data due to electrical noise or similar transients. This can interfere with normal temperature control functioning as, for example, by causing false starts of heating or cooling cycles, which themselves then result in unnecessary departures from equilibrium that have to be corrected. Wrong data can also cause false error designations leading to unnecessary lockouts or shutdowns or, at a minimum, ^' to user annoyance.

DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a method for detecting and disregarding random occurrences o invalid temperature data in a system for controlling th temperature of chemicals in an automatic film processor.

In accordance with the invention, a system fo controlling the temperature of chemicals in an automatic fil processor includes means for generating data corresponding t actual temperatures of the chemicals occurring at successiv times, and means for determining the validity of the generate data based on comparisons of the measured actual temperature with predictions as to what valid actual temperature state should be, given the heat gains (or losses) applied in th system during the time interval between measurements.

An embodiment of the invention, described in greate detail below, is employed with a general purpose radiographi

film processor having means for automatically transporting film through developer, fixer, wash and dryer Stations according to a selected one of a plurality of available film processing modes, each having an associated characteristic film transport speed and developer setpoint temperature. Data corresponding to measured actual developer temperatures occurring at successive times is generated for control and diagnostic purposes under microprocessor supervision, based on measurements taken at periodic time intervals by a temperature sensor in contact with developer flowing in a recirculation path. The measured actual temperatures are compared with predictions as to what the actual temperature states should be, considering the possible heat gains (or losses) per unit time for the applied heating (or cooling) cycle. If a measured actual temperature deviates from a corresponding predicted temperature by more than a predetermined tolerance factor, that measurement is disregarded for control and error diagnosis purposes. Similar non-valid state detection mechanisms are provided for fixer chemical and dryer air temperature data.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention have been chosen for purposes of illustration and description and are shown in the accompanying drawings, wherein: FIG. 1 is a perspective view of a processor in which a temperature control εyεtem incorporating the preεent invention can be employed;

FIG. 2 is a schematic representation of relevant elements of the processor of FIG. 1; FIG. 3 is a schematic diagram showing the developer and fixer recirculation paths;

FIG. 4 is a block diagram of the control system employed in the processor;

FIGS. 5-8 are flow diagrams of the operation_ of th system of FIG. 4; and

FIGS. 9 and 10 are graphical representations of tim variations of temperature over time during processor operatio for typical developer and fixer chemical solutions.

Throughout the drawings, like elements are referred to b like numerals.

MODE OF CARRYING OUT THE INVENTION The principles of the invention are illustrated, by wa of example, embodied in the form of a temperature contro system 10 (FIGS. 3-4) suitable for use with a processor 1 (FIGS. 1 and 2) having four user-selectable film modes for th automatic processing of photosensitive film F (FIG. 2) , suc as for the development of radiographic images for medica diagnostic purposes. Associated with each mode are defaul parameters for transport speed; developer and fixe replenishment volumes; developer, fixer and dryer setpoin temperatures; and so forth. Such parameters are stored i memory, but can be modified through user input. The processor 12 has a feed tray 14 positioned ahead o an entrance opening 15 (FIG. 1). Patient film F (FIG. 2 entered through entrance opening 15 is transported throug processor 12 along a travel path 16 (indicated by arrows i FIG. 2) by a network of conventional motor shaft-drive rollers 17, and eventually into a catch bin 18 at an exi opening 19. The path 16 includes travel through a developin station comprising a tank 21 filled with developer chemical a fixing station comprising a tank 22 filled with fixe chemical; and a wash station comprising a tank 23 filled wit wash water or comprising some other appropriate film washin device. Processor 12 also includes a drying station 2 comprising oppositely-disposed pluralities of air dispensin tubes 25 or other appropriate film drying mechanism.

Positioned proximate opening 15 is a sensor 26, such as a conventional reflective infrared LED sensor array., which provides a signal indicative of film width when film F is presented at the entrance opening 15. The film w ^' idth sensor 26 also provides an indication of the occurrence of passage of the leading edge and trailing edge of film passing point 26 of the processor 12, since the signal from the sensor 26 will change significantly as each leading and trailing edge is encountered. A second sensor 27, in the form of a reed switch or the like, may be provided to detect separation of the entrance rollers 28 to signal the beginning of transportation of film F along the path 16.

The temperature of developer chemical in tank 21 may be controlled by means of a developer recirculation path 30 (shown in dot-dashed lines in FIG. 3) having a pump 31 for drawing developer out of tank 21, passing it through a thermowell 33 incorporating a heater 34 or other suitable heating device, and then passing it back to the tank 21. The path 30 also includes means for cooling the developer, such as a solenoid valve 36 which may be operated to redirect the developer through a loop 37 in heat exchange relationship with cooling water in water tank 23. The flow of water in tank 23 (see dot-dot-daεhed lines in FIG. 3) is under control of a solenoid valve 39. A temperature εensor 35 (FIG. 4) is provided in the tank 21 or recirculation path 30 to monitor the temperature of the developer. The sensor 35 may, for example, be a thermocouple provided in the thermowell 33. Developer temperature may be displayed on a panel 38 (FIG. 1) located externally on the processor 12. The temperature of fixer chemistry may be controlled in a similar manner by means of a fixer recirculation path 40 (shown in solid lines in FIG. 3) having a pump 41 for drawing fixer out of tank 22, passing it through a.. thermowell 43

incorporating a heater 44 or other suitable heating device, and then passing it back to the tank 22. A temperature sensor 45, such as a thermocouple similar to thermocouple 35, is provided in the tank 22 or recirculation path 40 ^' to monitor the temperature of the fixer. Maintaining the setpoint temperature of the fixer r$ less critical than maintaining the setpoint temperature of the developer, so no cooling loop is provided.

The temperature of air in the dryer 24 can be maintained by energizing a blower motor 48 and air heater 49 (FIG. 4) to drive warm air through the tubes 25 (FIG. 2) and across the surface of film F. A temperature sensor 52, similar to thermocouple 35 or 45, may be located in the air path to monitor dryer air temperature. It will be appreciated that other ways of controlling processor chemistry and dryer temperatures may be employed.

Recirculation of developer and fixer takes place when the developer and fixer tanks 21, 22 are full. The "full" condition is detected by level sensing sensors 50, 51 (FIG. 4) located in communication with the tanks 21, 22. Developer and fixer replenishment occurs automatically if the level falls below a predefined desired level. This is accomplished for the developer by energizing a replenishment pump 53 (FIG. 3) connected at its input side to a supply of replenishment developer 54 and at its output side to a filter aεεembly 55 located in fluid communication with the developer tank 21. For the fixer, replenishment is similarly accomplished by energizing of a replenishment pump 56 connected at its input side to a supply of replenishment fixer 57 and at its output side to a filter assembly 58 located in fluid communication with the fixer tank 22.

The sensors 50, 51 nay be of a type having one contact in the form of a probe •xposed to the solution and anothe

contact grounded to the case of the heater 34 or 4-3. The probe can be located to monitor solution level in the main tank 21 or 22 or in an associated level-sensing auxiliary reservoir. When the probe becomes immersed in solution, a path is provided to ground and the resistance of the sensor circuit is lowered. The value of the lowered resistance indicates the level of the solution.

FIG. 4 illustrates a control system usable in implementing an embodiment of the present invention. As shown, a microprocessor 60 is connected to direct the operation of the processor 12. Microprocessor 60 receives input from the user through a mode switch 61 as to what processor mode of operation is desired. The system can be configured to enable the user to select among predesignated modes, such as "Kvik" or "K/RA," "Rapid," "Standard," or "Extended" modes, each having predetermined associated film path speed and chemistry temperature parameters prestored in a memory 62. The system can also be configured to permit a user to input a desired path speed and temperature directly into memory 62.

One way to implement mode switch 61 is by means of an alphanumeric keypad associated with display 38 (FIG. 1) for providing programming communication between the user and the microprocessor 60. For example, a function code can be entered to signal that mode selection is being made, followed by a selection code to deεignate the εelected mode. Alternatively, a function code can be entered for film path speed or chemiεtry temperature, followed by entry of a εelected speed or temperature εetting. Another way to implement switch 61 iε by eanε of a plurality of push button or toggle switches, respectively dedicated one for each selectable mode, and which are selectively actuated by the user in accordance with user needs.

Microprocessor 60 iε connected to receive input information from the film width sensor 26, the entrance roller sensor 27, the developer, fixer and dryer temperature sensors 35, 45, 52, the developer and fixer level sensors 50, 51, and from various other sensors and feedback controls. The sensors 26, 27 provide the microprocessor 60 with information on the leading and trailing edge occurrences and the width of film F. This can be used together with film speed from a sensor 63 (FIG. 4) which measures the speed of shaft 65 of motor 67 used to drive the rollers 17 (FIG. 2) , to give a cumulative processed film area total that guides the control of chemiεtry replenishment. The entrance roller sensor 27 signals when a leading edge of film F has been picked up by the roller path 16. This information can be used together with film speed and known length of the total path 16 to indicate when film F is present along the path 16.

As shown in FIG. 4, microprocessor 60 is connected to heater control circuitry 68, 69, cooling control circuitry 70, replenishment control circuitry 72, 73, dryer control circuitry 74, drive motor control circuitry 75 and annunciato control circuitry 77. Heater control circuitry 68, 69 i connected to heaters 34, 44, and cooling control circuitry 7 is connected to valves 36, 39 (FIGS. 3 and 4), to control th temperature of the developer and fixer flowing in th recirculation paths 30, 40 (FIG. 3) and, thus, the temperatur of the developer and fixer in tanks 21, 22. Replenishmen control circuitry 72, 73 is connected to valves 53, 56 t control the repleniεhment of developer and fixer in tankε 21, 22. Dryer control circuitry 74 is connected to dryer blowe motor 48 and air heater 49 to control the temperature of ai in dryer 24. Drive motor control circuitry 75 iε connected t motor 67 to control the speed of rotation of drive shaft 6 and, thus, of rollers 17. This regulates the speed of trave

of film F along film path 16 and, thus, determines the length of time film F spends at each of the stations (i.e., controls development, fixer, wash and dry times) . Annunciator control circuitry 77 is connected to control the on/off cycles of annunciators in the form of a "Wait" light 78, a "Ready" light 79, and an audible alarm or buzzer 80.

The invention takes into account that, under normal functioning of heating (or cooling) cycles, the heat gain (or losε) per unit time Q experienced by the developer or fixer εolutionε will follow general principleε of thermodynamics, as follows:

Q = (rate of energy influx to the solution)- (rate of energy influx from the solution) . Thus, for a given mass m of solution having a εpecific heat C , the amount of heat per unit time needed to raise the temperature of the solution by an increment ΔT can be expresεed aε:

Q = mC _p ΔT. A heat gain (or loεε) per unit time applied for a time increment Δt to the εame solution can thus be expressed as:

QΔt = mC _p ΔT. So, applying a known heat rate Q for a time Δt to a known masε m of εolution having an initial temperature T, εhould, under normal circumεtanceε, reεult in a new temperature T-, defined by:

^{2 x} mC _p

Mathematical modeling of the thermal system of an automatic processor such as the processor 12 iε described in

"Ambient Water Thermal Control System" by Kenneth W. Oemcke, Department of Mechanical Engineering, Rochester Institute of

Technology, Rochester, New York, July 1978. Applying such

- 13 - techniques to the developer and fixer recirculation paths 30, 40 of FIG. 3, yields the following expressionε for normal operation of heating (or cooling) cycles for developer and fixer in processor 12:

T^ J- _Q J * _>_(-„----) _

-7 'D-C*-FD

and

£_(_-.---,) τ _n - -77 F-C^FF

expressed in terms of developer and fixer temperatures T _D2 , T _F2 , and T _D1 , T _F1 taken at times t„ ₂ , t _F2 and t ₀₁ , t _f1 ; and flow rates m., m _F of developer and fixer ^' hrough the thermowells 33, 43, respectively. The replenishment cycles function to keep the mass of solution flowing in the paths 30, 40 constant fo a particular operating mode.

The operation of the control εyεtem 10 in accordance wit the invention iε described with reference to FIGS. 5-10.

When power iε applied at εtart-up, or proceεεor 12 i reεet to a different mode (100 in FIG. 5) , the εyεtem i initialized and system variables, including film speed an setpoint temperatures, are set (102) . The wash water solenoi 39 is energized, allowing water to flow into the tank 23 ^" ; an the developer and fixer solution levels are checked by readin sensors 50, 51 (103). If the levels are low, replenishmen cycles are activated, as necessary, energizing pumps 53, 56 t fill the tankε 21, 22 (104, 106). If the levelε do not reac their preset target levels within a predetermined time (e.g., count 1 = 1 = 4 minutes), a tank fill error occurs (107, 108). In the absence of activation by the user of anOverride (109),

the fill error signal will sound a buzzer 80 (FIG. 4), "disable the drive motor 67 (FIG. 4) , or otherwise inhibit the feeding of fresh film F (110) until the error is cleared. if the correct levels are reached, pumps 53, 56 are deenergized (112) and recirculation pumps 31, 41 are energized to flow the solutionε along the recirculation pathε 30, 40 (114). In the εhown embodiment, the pumpε 31, 41 are magnetically coupled on opposite sides of a εingle recirculation motor 84 (FIG. 3) . It will be appreciated however, that separate pump motors can be used.

Microcomputer 60 uses algorithms and controls to monitor the temperatures of the developer, fixer and dryer air baεed on signals received from the sensors 35, 45, 52. The temperatures of developer and fixer within the pathε 30, 40 εhould increaεe at normal rates following an initial warm-up period of several minutes after start-up or reset. FIGS. 9 and 10 illustrate the relationship between temperature and time for the developer and fixer chemicals for normal heating

(and cooling) cycles from system start-up through εuccessful attainment of setpoint temperature.

The developer, fixer and dryer thermiεtorε 35, 45, 52 may εuitably be connected for εhared component processing, to multiplexer circuitry 86 and an analog-to-digital (A/D) converter 87 (FIG. 4). The multiplexer circuitry 86 sets the channel and voltage range for the A/D converter 87.' The microproceεεor 60 checkε for two different errors with the thermistorε: wrong A/D temperature converεionε, and opened or shorted thermistors. The temperature conversions are monitored through a precision resistor 89, which is read at periodic intervals to verify the accuracy of the A/D conversion. If the value of resistor 89 is not correct for a predefined number of consecutive readings, the A/D converter 87 iε considered faulty. An opened or shorted thermistor is

determined by reading an internal A/D in the microprocessor 60 (line 88 in FIG. 4) at the same time as the control A/D converter 87 for the developer, fixer and dryer sensor channels. If the readings on the internal A/D fall outside of the allowed range for a predefined number of consecutive readings, the thermistor "is considered faulty. An error in the multiplexer circuit can be detected by comparing readings of the resistor 89 taken using the external A/D converter 87 and using the internal A/D converter 88 (119, 120). These checks are not performed until a time delay period of e.g., three minutes, has elapsed after power-up. This delay prevents open thermistor errors due to cold solution temperatures or cold ambient. Developer Temperature Control While the developer iε recirculating (114) , thermistor 35 in the thermowell 33 monitors actual developer temperature T _DA at time t ₀ (116). The resistance of the thermistor 35 changes inversely with the temperature of the solution. This data iε sent to the microprocesεor 60, which controlε the heating and cooling εyεtemε.

The actual developer temperature T _DA is determined by performing an analog-to-digital (A/D) conversion on the resistance of the thermistor 35. This data iε then converted to a temperature of "C or "F by meanε of a εoftware algorithm. The temperature is then compared to the setpoint temperature T _DS previously stored in memory 62 to determine if heating or cooling is required (118) . The temperature iε read periodically at intervalε of Δt, e.g., every 1/2 or 3/4 secon . Optimum processing quality occurs when the developer temperature iε maintained substantially at its setpoint temperature T _0$ . A tolerance of ±X , determined by uεer input or default, nay be allowed (118) . If the developer iε belo

setpoint T _DS , the heater 34, located inside the thermowell 33, is controlled to pulse on and off at a duty cycle defined by microprocessor 60 based on the temperature data repeived from the thermistor 35 (120, 121). The heating of the developer is controlled by a proportional method. Heater 34 is turned on full until the temperature T _DA measured by sensor 45 iε within 0.5* of the preestabliεhed setpoint T _DS . This is shown by region I in FIG. 9. Region I iε characterized by an initial portion 91 having a steep rise due to the effect of heater 34 of developer in thermowell 33 prior to recirculation; a second, reduced slope portion 92 which is influenced by the cooling effect of introduced replenishment solution and heat losses due to residual ambient cooling; and, finally, a third region 93, starting about 4 minutes into the cycle, marked by an almost linear rise of net heat gain due to the heater 34 over system and ambient heat losses. Heater 34 then operates on a duty cycle of 75% over a region II shown in FIG. 9, until the temperature T _DA measured by sensor 45 comes within 0.3' of the setpoint T _DS . Heater 34 then operates on a duty cycle of 50% over a region III, until the temperature _Ό is within 0.1* of the setpoint T _DS . And, finally, heater 34 operates on a duty cycle of 25% in a steady εtate region IV, until the εetpoint temperature T _DS iε reached. When the εetpoint temperature T _DS iε reached, the developer heater εhutε off (122). FIG. 9 iε plotted for a processing mode having a developer setpoint temperature of T _os = 95'F (35*C) with time marked in intervals of 75 readings of 3/4 second spacing each, and with temperature marked in intervals of 500 in decimal on a 12-bit A/D converter 87 (which corresponds to interval εpacings of about 1.6* each). The origin of the temperature axiε occurε at 90 ^C F (32.2'C) .

If the developer temperature T _0A sensed by the sensor 45

- 17 - iε 0.3 ^* or more than the εetpoint T _DS for J=5 consecutive readingε, a cooling cycle iε activated. If not already energized, the waεh water εolenoid 39 is activated to flow water in the tank 23 around the heat exchanger loop 37 (123, 124). The developer cooling εolenoid 36 iε then energized (125) , allowing developer in the recirculating path 30 to circulate through the loop 37. The cooler water in the tank 23 surrounding the heat exchanger 37 acts to cool the developer. The cooler developer then returns to the main recirculation path 30 and back to the tank 23. The cooling cycle continues until the developer temperature T _0A drops to 0.1 ^* below the setpoint T _os for one reading of the developer thermistor 35 (127) . The developer cooling εolenoid 36 then deenergizes, shutting off the developer εupply to the heat exchanger 37 (128) . If pump 39 waε not already energized when the cooling cycle began, it too iε εhut off (129, 130). For most effective functioning of the developer cooling εyεtem, the temperature of water flowing in the waεh tank 23 should preferably be at a temperature 10'F (6 ^e C) or more below the operating setpoint T _DS of the developer temperature.

The developer heating and cooling εyεtems are responsible for maintaining the developer at the current processing mode temperature εetpoint T _DS under all operating conditionε. The developer εolution should stabilize at the setpoint temperature T _DS within 15-20 minutes after start-up, and within 5 minutes after a mode change. In accordance with the out-of- rate error detection procedure of U.S. patent application

Serial No. , the rate of change of temperature of the developer is monitored (139, 140) to ensure that it iε within acceptable limits. If the rate of change for the developer temperature iε not within the tolerance of normall expected rate of change, the processor will display an erro message (142, 143). This differs from conventional method

- 18 - which look only at absolute temperatures to determine^whether the measured actual temperature T _DA exceeds a preεpecified maximum developer temperature limit T _DUL (FIG. 9) at any time. If it does, an overtemperature error occurs. Absolute temperature overtemperature protection is provided in the depicted embodiment (145, ^* - 146) . However, in addition, for each heating or cooling cycle, the actual rate of change in developer temperature R_, _A = (T _D2 - T _D1 )/(t _D2 - t _D1 ) that actually occurs (200) iε compared with a predetermined acceptable change in developer temperature R_, _s (R_ _H or R_, _c ) that should occur if that heating or cooling cycle is functioning normally. If the difference between the predicted change and the actual change exceeds a preestabliεhed tolerance ±Y ^e per εecond, a rate error iε flagged. A "loss of developer heating ability" or "loεε of developer cooling ability" error iε diεplayed. Theεe errors are cleared when either the rate corrects itself or the εetpoint temperature T _DS is reached (115). Should the error persist and not correct itself, a buzzer signal, drive transport lockout or other fresh film feed inhibit routine can be invoked, subject to a user selectable override.

If thermistor 35 is open- or short-circuited, or the temperature control A/D converter is not operating correctly, an "unable to determine developer temperature" error message will be diεplayed (148, 149) . This error will not normally be cleared unlesε the proceεsor iε deenergized and then energized again.

The cooling rate iε checked aε long aε cooling iε needed. The heat rate iε checked when the developer iε on full; the temperature of the εolution iε above 8 "F (29*C) or ten minute timeout occurε; and the repleniεh pumpε are off. For the depicted embodiment, the minimum heating rate. ^• R _DH (139) calls for en increase of 2.0* every 2 minutes; and the minimum

- 19 - cooling rate R _p . (140) calls for a decrease of 0.1* -every 3 minutes.

Electrical noise or similar transients experienced by the electrical control system 10 can lead to random occurrences of invalid temperature measurements T _0A (116) . Comparisons of erroneous values of T _DA vith setpoint temperature τ _DS for heating or cooling cycle control purposes (118, 127), can lead to unintended heating or cooling cycle activations or deactivations. Such unintended activity may upset the temperature balance of the system, reguiring otherwise unnecessary additional corrective heating or cooling operations. Furthermore, comparisons of erroneous values of T _0A with preestabliεhed allowable temperature limits T _DUL (145) , or of rates R _j>A based on erroneous values of T _DA with predetermined acceptable rates R_. _H , R-, _c (139, 140), can lead to false error designations (146, 142, 143), leading to unintended interference with normal processing.

In accordance with the invention, the validity of the temperature T _DA of developer measured at a time t _D iε verifie to determine its correspondence with a temperature T _D predicted for the developer for the same time t _D , given known εtarting temperature T ₀₁ at time t _D1 and known heat gai (or loεε) relationεhipε applicable for the heating or coolin cycle to which the developer is εubjected during the tim interval from t _D1 to t _D . Because the developer temperatur changes relatively slowly, the temperature εtate of th developer can only change by a certain amount in any give time interval for any given heating or cooling cycle. Thus, a measured temperature T _0A that deviates from the predicte value T _DP by more than a preestabliεhed tolerance ±Z corresponds to a developer temperature state which canno exist and iε, thuε, invalid. In accordance with th invention, random occurrences of erroneouε data T _0A indicativ

of non-valid temperature εtateε are identified and disregarded for control and error diagnoεiε purpoεeε.

The εtepε for exemplary implementation of a developer temperature validating process in the procedure of FIG. 5 are shown in FIG. 6. The actual temperature T _DA of developer at time t _D iε read, as before (116) . The values of T _D2 , t _D2 are then set to T _0A , t _D (200) , and an actual change rate R-, _A iε calculated (201) . However, before the measured actual temperature T _DA or rate R-, _A are used in control or error determination comparisonε (148, 145, 118, 127, 139, 140), a data validating procedure iε undertaken, as shown in FIG. 6. A suitable place for this to occur is between the steps 201 and 148 of FIG. 5.

The verification process may be implemented εo that it takeε place only after a preεet time (determined by count 13 = T minuteε) haε elapsed since start-up or mode change (202- 203, FIG. 5, and 204-207, FIG. 6). A predicted temperature T _DP at time t _D = t _β2 is determined (210) based on an applicable heat gain (loss) factor Q. chosen in accordance with whether a heating cycle, cooling cycle or neither is active (212-216) . The measured actual temperature T _DA = T _D2 at time t _D2 is then compared with the determined predicted temperature T _DP at the same time t _D2 (218) . If the eaεured actual temperature T _D2 iε within acceptable tolerance ±Z* of the predicted temperature T _pp , itε validity iε affirmed, and that data is utilized in the control and error diagnosis comparisonε (148, 145, 118, 127, 139, 140) . However, if the measured temperature T _D2 is outside the acceptable tolerance ±Z ' , control and error diagnosis comparisonε are circumvented until a valid T _M is encountered (218, 220).

If values of meaεured actual temperature T _0λ continue to deviate beyond acceptable limits from predicted values, indicating that the error is not random (i.e. occurs more than

R times in a row) (221-222), an error is signalled (224) to show that non-valid temperature states are being continuously indicated.

The effect of implementation of an invalid data detection and elimination procedure in the developer temperature control process, as described, is-.to provide a guardband 95 (shown in dot-dashed lines in FIG. 9) about the plot of developer temperature vs. time. Any isolated data point occurring outside of the guardband 95 will be disregarded fo temperature control and error diagnosis purposes. Fixer Temperature Control

The replenishment and temperature control cycle associated with the fixer tank 22 are similar to thos associated with the developer tank 21. Tank 22 is both fille and replenished automatically from a connection 57 to a suppl of fresh fixer solution. Like the developer, when tank 22 i full, fixer is recirculated continuously by a recirculatio pump 41 through a thermowell 43 where a thermistor 45 monitor the temperature of the solution. When the fixer solution iε circulating in path 40, heater 44 in the thermowell 43 maintains the temperature o the solution to increase its effectiveneεε. This i especially important to support the faster processing modes The duty cycle of the fixer heater 44 is not regulated lik that of the developer heater 34. The fixer temperature T _fA i determined by performing an analog-to-digital (A/D) converεio on the reεiεtance of the thermistor 45 using the sam multiplexer circuitry 86, A/D converter 87, and internal A/ converter 88 aε for the developer (150) . Thiε data iε the converted to a temperature in 'F or 'C by microproceεεor 60 b means of a software algorithm. The temperature is the compared to the setpoint T _FS stored in memory 62 to determin if heating is required (152). FIG. 10 illustrateε the heatin

- 22 - of fixer to a εetpoint temperature T _FS of about 90*F _ ₃₂ .2'C) on a plot having the same interval markings aε FIG. 9, except that the origin on the temperature axis is displaced downward by 7 intervals. The fixer, which operates more effectively at higher temperatures, does not have to be cooled. The fixer heater 45 operates at full capacity when the fixer is below the εetpoint T _FS (152, 154). When the temperature T _FA iε above the εetpoint, the heater is turned off (155) . Like the developer, the fixer solution should stabilize at the setpoint temperature T _FS within 15-20 minutes after start-up, and within 5 minutes after a mode change.

The rate at which the fixer solution is heated is checked (156) . If the rate of change R _FA for the fixer temperature T _fA is not within normal anticipations, the processor 12 will display a "losε of fixer heating ability" error message (158) . The minimum acceptable heating rate for the depicted embodiment is an increase of 2.0' every 2 minutes. This error is cleared when either the rate corrects itεelf or, unleεε the film feed inhibit function iε active, the fixer setpoint temperature T _FS is reached. The fixer heat rate error is checked when the fixer is on full; the temperature is above 84"F (29*C) or ten minute timeout occurs; and the replenish pumps are off. If the thermistor 45 iε opened or shorted, or the temperature control A/D is not working, an "unable to determine fixer temperature" error will be diεplayed (160, 161).. An "overtemperature" error will occur if the fixer temperature F _FA exceedε a preeεtabliεhed maximum allowable upper limit T _FϋL (163, 164). These errors are normally not cleared unleεε the proceεεor 12 iε deenergized and then energized again.

In accordance with the invention, the fixer temperature

control proceεε εhown in FIG. 5 can be augmented, as shown in FIG. 7, to provide for invalid data detection and disregard. The augmentation iε similar to that utilized in. connection with the developer temperature control process, described above in reference to FIG. 6. The actual temperature τ _FA of fixer at time t _F is read, aε before (150) . The values of τ _F2 , t _F2 are then set to T _FA , t _F (230) , and an actual change rate R _FA iε calculated (231). However, before the meaεured actual temperature T _FA or rate R _FA are uεed in control or erro determination compariεonε (160, 163, 152, 156), a data validating procedure iε undertaken, aε εhown in FIG. 7, between the εtepε 231 and 160 of FIG. 5.

Aε with the developer temperature data validit verification process, the fixer temperature validit verification may be implemented so that it only takes plac after a preset time (determined by count 14 = U minutes) ha elapsed since start-up or mode change (202-203, FIG. 5, an 234-237, FIG. 7). A predicted temperature T _FP at time t _F = t _F is determined (24) based on an applicable heat gain factor Q chosen in accordance with whether a heating cycle is active or not (242-244). The meaεured actual temperature T _FA = T _F2 a time t _F2 iε then compared with the determined predicte temperature T _FP at the εa e time t _F2 (246) .

If the meaεured actual temperature T _F2 iε withi acceptable tolerance of the predicted temperature T _Fp , it validity iε affirmed, and that data iε utilized in the contro and error diagnosis comparisonε (160, 163, 152, 156) However, if the meaεured temperature T _r2 iε outεide th acceptable tolerance, control and error diagnoεiε compariεon are circumvented until a valid T _rA is encountered (246, 248)

If values of measured actual temperature T _fA continue t deviate beyond acceptable limits from predicted values, a error is signalled (249) to show that non-valid fixe

temperature stateε are being continuously indicated.

The effect of implementation of an invalid data detection and elimination procedure in the fixer temperature control procesε, aε deεcribed, iε to provide a guardband 96 (εhown in dot-daεhed lineε in FIG. 10) about the plot of fixer temperature vε. time. Any iεolated data point occurring outεide of the guardband 96 will be disregarded for temperature control and error diagnosis purposes. Drver Air Temperature Control As film F is transported through the dryer 24, air tubes 25 circulate hot air across the film F. The tubes 25 are located on both sides of the dryer 24 to dry both sides of the film at the εame time. The dryer heater ^' 49 heats the air to a setpoint temperature T _AS within the range of 90-155'F (38- 65.5'C) as set by the user or mode default parameterε. The actual temperature T _M in the dryer iε εensed by a thermistor 52 using the εame multiplexer and A/D circuitε 86, 87.

The air temperature T _AA iε determined by converting the reεistance of thermistor 52 into ^e F or ^e C (167) . This value is then compared to the setpoint T _AS (169) . If the temperature ^ is below the setpoint T _AS , the dryer blower 48 and dryer heater 49 are turned on (171, 172) . The blower 48 activates first, with the heater 49 following (this preventε damage to the heater) in reεponεe to activation of the vane εwitch 82 by the blower air (173). The heater 49 operateε at full capacity. When the temperature T _AA iε above the εetpoint T _AS , the dryer heater 49 iε turned off (175) . The actual rate R _AA at which the air in the dryer iε heated iε checked (177) . For the depicted embodiment, the minimum acceptable heating rate iε an increase of 0.5" every 2 minutes. If the rate is not correct, an "inoperative dryer" error is diεplayed (178) . The heat rate error is checked when the dryer heater iε operating; film iε not preεent in the procesεor; and after initialization

is completed at power-up. If the dryer temperature T^ exceeds the maximum temperature value T _AUL of the A/D converter (approximately 167 ^* F), an overtemperature condition exists (179) . A "dryer overtemperature" data error will be diεplayed and the processor will shut down after the last film exits (181). If the thermistor 52 iε opened or shorted, or the temperature control A/D converter 87 is not operating correctly, an "unable to determine dryer temperature" error message is diεplayed (183, 184). Thiε error normally remains unless the processor is deenergized and then energized again. If the dryer εetpoint temperature T _AS iε changed to a higher value, a "dryer underset temp warning" iε diεplayed until the new εetpoint is reached (185) .

Aε for the developer and fixer temperature control processes, the dryer air temperature control process εhown in FIG. 5 can be augmented, aε εhown in FIG. 8, to provide for detection and disregard of invalid data. Actual temperature T _AA at time t _A iε read, aε before (167) . The valueε of T _A2 , t _A2 are then εet to T _A , t _A (250) , and an actual change rate R _AA iε calculated (251) . However, before the meaεured actual temperature T _AA or rate R _AA are uεed in control or error determination compariεonε (169, 183, 179, 177), a data validating procedure iε undertaken, aε εhown in FIG. 8, between the steps 251 and 169 of FIG. 5. A predicted temperature T _AP at time t _A = t _A2 iε determined (253) baεed on an applicable heat gain factor Q _A choεen in accordance with whether a heating cycle iε active, or not (254-256) . The meaεured actual temperature T^ = T _A2 at time t _A2 iε then compared with the determined predicted temperature T _AP at the εame time t _w (258). If the meaεured actual temperature T _w is within acceptable tolerance of the predicted temperature T _AP , its validity is affirmed, and that data is utilized in the control and error diagnosis comparisons (169,

183, 179, 177). However, if the measured temperature T _A2 is outside the acceptable tolerance, control and error diagnosis compariεonε are circumvented until a valid T _M is -encountered (258, 259). If valueε of the meaεured actual temperature T _M continue to be invalid, an error iε εignalled (260) to show that non-valid dryer air temperature states continue.

Aε film F leaveε the dryer 28, it paεεeε through the exit opening 19 where it iε tranεported out of the interior of the proceεεor 12 and into the top receiving tray 18. If no new film F enters the procesεor, the proceεεor will enter a εtandby mode approximately 15 εecondε after a film haε exited. In the εtandby mode the water εupply iε turned off, unleεε needed for developer cooling; the developer, fixer and dryer temperatureε are maintained at their setpoints T _DS , T _FS and T _A _; and the drive motor 67 iε changed to εtandby operation.

Thoεe εkilled in the art to which the invention relateε will appreciate that other εubεtitutionε and modificationε can be made to the deεcribed embodiment without departing from the spirit and εcope of the invention aε deεcribed by the claimε below.