Source: http://www.google.com/patents/US5734407?dq=7,194,691
Timestamp: 2017-04-26 20:24:33
Document Index: 739242122

Matched Legal Cases: ['art 105', 'art 106', 'art 107', 'art 108', 'art 106', 'art 108', 'art 108', 'art 109', 'art 101', 'art 108', 'art 110', 'art 102', 'art 101', 'art 200', 'art 200', 'art 100', 'art 200', 'art 120', 'art 120', 'art 120']

Patent US5734407 - Image quality control at restart of image forming apparatus - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inPatentsWhen a control part is restarted, an average of a stored standard operation quantity and a stored operation quantity immediately before a stop of the control part is calculated. The average operation quantity (for instance, laser power) is applied to an image output part, and a resulting control quantity...http://www.google.com/patents/US5734407?utm_source=gb-gplus-sharePatent US5734407 - Image quality control at restart of image forming apparatusAdvanced Patent SearchTry the new Google Patents, with machine-classified Google Scholar results, and Japanese and South Korean patents.Publication numberUS5734407 APublication typeGrantApplication numberUS 08/621,614Publication dateMar 31, 1998Filing dateMar 26, 1996Priority dateMar 31, 1995Fee statusLapsedPublication number08621614, 621614, US 5734407 A, US 5734407A, US-A-5734407, US5734407 A, US5734407AInventorsKunio Yamada, Kiyotaka IshikawaOriginal AssigneeFuji Xerox Co., Ltd.Export CitationBiBTeX, EndNote, RefManPatent Citations (11), Referenced by (17), Classifications (11), Legal Events (6) External Links: USPTO, USPTO Assignment, EspacenetImage quality control at restart of image forming apparatus
US 5734407 AAbstract
When a control part is restarted, an average of a stored standard operation quantity and a stored operation quantity immediately before a stop of the control part is calculated. The average operation quantity (for instance, laser power) is applied to an image output part, and a resulting control quantity (for instance, a development density) is measured. A control rule retrieval unit calculates adaptabilities of respective control rules with respect to the measured control quantity, thereby synthesizing an application control rule. A new operation quantity is determined based on the application control rule and an error of the measured control quantity from a target value.
1. A control apparatus for use with a system having a status and outputting a control quantity, comprising:operation quantity output means for applying an operation quantity to the system being controlled; control quantity measuring means for measuring the control quantity output by the system in response to the operation quantity; control case memory means for storing control cases, each control case including an operation quantity, a corresponding control quantity being output by the system in response to the operation quantity, and a corresponding system status; system status quantity measurement means for measuring the system status; cluster formation means for forming clusters of control cases having similar system status quantities; control rule extracting means for forming a control rule for each said cluster of control cases to produce a plurality of control rules; and operation quantity calculating means for comparing each of said control rules formed by the control rule extracting means with an immediately preceding control result, weighting each of said control rules in accordance with the comparison result and averaging a sum of said weighted control rules to thereby synthesize a new control rule, determining, by using the synthesized new control rule, a new operation quantity, which when applied by the operation quantity output means will cause a new control quantity to equal a predetermined target value, and supplying the new operation quantity to the operation quantity output means, wherein when the system or a control operation thereon is restarted after a stop thereof, the operation quantity calculating means performs a given conversion on an operation quantity of said control case immediately before the stop, which causes the operation quantity output means to output the converted operation quantity, and compares each of said control rules with a control result obtained in response to the converted operation quantity. 2. An image forming apparatus for controlling an operation quantity so that a control quantity relating to image quality becomes a target value, said image forming apparatus comprising:means for setting the target value; means for measuring the control quantity; means for detecting a restart of the image forming apparatus; memory means for storing, as control rules, a plurality of functions defining a relationship between the operation quantity and the control quantity, each control rule being determined based on a given number of cases each including a particular operation quantity actually applied in the image forming apparatus and a corresponding control quantity actually measured; application control rule generating means for generating an application control rule being used to calculate the operation quantity based on the measured control quantity by combining at least part of the plurality of functions; standard operation quantity storing means for storing a standard operation quantity in a standard status of the image forming apparatus; means for calculating, in response to detection of the restart of the image forming apparatus by the restart detecting means, a new operation quantity based on the standard operation quantity and an operation quantity that is determined based on the application control rule and a difference of the measured control quantity from the target value; and means for changing the operation quantity based on the calculated new operation quantity. 3. The image forming apparatus according to claim 2, wherein the calculating means calculates an average of the standard operation quantity and the operation quantity that is determined based on the application control rule and the difference of the measured control quantity from the target value.
4. The image forming apparatus according to claim 2, wherein the standard status of the image forming apparatus is a status that a temperature and a humidity are both predetermined values.
The present invention relates to an image forming apparatuses of various types such as an electrophotographic type and an ink jet type, and a control method therefor. In particular, the invention is intended to allow control for keeping the image quality at a given level to be carried out at a low cost with high accuracy, as well as to greatly reduce or substantially eliminate man-hours necessary for data collection and design optimization in developing a new product.
The present invention aims at eliminating the above-mentioned problems found in the conventional image forming techniques. Accordingly, it is an object of the invention to provide an image forming technique which is capable of controlling an operation amount simply and accurately with no need for engineers to grasp various environmental conditions previously, thereby being able to reduce man-hours for development to a great extent.
Another object of the invention is to provide a technique which, even when a vast number of image forming apparatuses are introduced into the market and they are respectively used in various ways and the parts thereof are replaced as the occasion demands, can maintain the quality of images formed by the individual image forming apparatuses at a high level.
A further object of the invention is to provide a technique which, when a system to be controlled is restarted, can reduce influences caused by the status change of the system before and after the system to be controlled is restarted, and thus can control the system quickly with a high accuracy from the beginning of the restart operation thereof.
To attain the above objects, according to the invention, there is provided an image forming apparatus which is arranged to control an operation quantity so that a control quantity relating to the image quality becomes a target value, the image forming apparatus comprising: means for setting the target value; means for measuring the control quantity; memory means for storing, as a control rule or rules, one or a plurality of functions of the operation and control quantities which functions are determined based on operation quantities actually applied in a series of image forming processes and corresponding control quantities actually measured; application control rule generating means for generating an application control rule to be used to calculate the operation quantity based on the control quantity from the one function or by combining at least part of the plurality of functions; means for varying the operation quantity in accordance with an error between the control quantity and the above target value; status transition judging means for judging whether a transition of a status of a main body of the image forming apparatus has occurred; and means for determining a new function from operation actually applied and control quantities actually measured in a series of image forming processes in response to a judgment output of the status transition judging means, and for causing the memory means to store the new function as a new control rule, wherein the application control rule generating means generates a new application control rule with the new control rule taken into account.
The image forming apparatus may further comprise status transition judging means for judging whether a transition of the status of the image forming apparatus main body has occurred, means for generating a new control rule in response to a judgement output of the status transition judging means, and means for causing the memory means to store the thus generated new control rule in place of a control rule that has not been selected for a longest time by the selecting means.
To attain the above objects, according to a further aspect of the invention, there is provided an image forming apparatus for controlling an operation quantity so that a control quantity relating to image quality becomes a target value, said image forming apparatus comprising: means for setting the target value; means for measuring the control quantity; means for detecting a restart of the image forming apparatus; memory means for storing, as control rules, a plurality of functions of the operation quantity and the control quantity each of which functions is determined based on a given number of cases each including an operation quantity actually applied in the image forming apparatus and a corresponding control quantity actually measured; application control rule generating means for generating an application control rule to be used to calculate the operation quantity based on the measured control quantity by combining at least part of the plurality of functions; standard operation quantity storing means for storing a standard operation quantity in a standard status of the image forming apparatus; means for calculating, in response to detection of the restart of the image forming apparatus by the restart detecting means, a new operation quantity based on the standard operation quantity and an operation quantity that is determined based on the application control rule and an error of the measured control quantity from the target value; and means for changing the operation quantity based on the calculated new operation quantity.
FIG. 1 is a block diagram of a first embodiment which corresponds to the principle operation of the present invention;
FIG. 26 is a block diagram showing the configuration of a control part in a third embodiment of the invention;
FIG. 27 is a graph showing a relationship between an operation quantity and a control quantity before and after a system to be controlled is restarted in a case where an operation quantity set value itself before the system is stopped is used as the operation quantity for an operation after the restart;
FIG. 28 is a graph showing a relationship between an operation quantity and a control quantity before and after a system to be controlled is restarted in a case where an average value of an operation quantity set value before the system is stopped and a standard operation quantity is used as the operation quantity for an operation after the restart; and
FIG. 29 and 30 are graphs each showing a relationship corresponding to that of FIG. 28 which relationship is obtained under different conditions from those of FIG. 28.
The control rule stored in the control rule memory part 105 is supplied to a control rule deviation computing part 106, in which it is used to compute the adaptabilities of the respective control rules as will be described later. The control rule is also supplied to a rule select part 107, while part or all of the control rules are supplied to an application control rule output part 108.
The control rule deviation computing part 106, for each of the control rules, finds a deviation or a difference between a control quantity expected when the control rule is applied to an operation quantity in a given image forming process (for example, the last or previous image forming process to be measured) and an actual control quantity in the given image forming process. The difference is supplied to the application control rule output part 108. Responsive to this, the output part 108 combines together the control rules using a weight which increases as the difference decreases, and outputs the resultant combination as an application control rule which can be applied to determine an operation quantity. The combination of the control rules can be achieved, for example, by adding together functions representative of the control rules with weighting.
An operation quantity correcting part 109 varies the operation quantity of the operation part 101 in accordance with the application control rule that is output by the application rule output part 108. That is, an error between a target value set by an target value setting part 110 and a control quantity measured by the control quantity measuring part 102 is detected by an error detector 111, and an operation quantity (or a variation thereof) to cancel this error is computed according to the application control rule. The thus computed operation quantity is then added to the operation part 101.
FIG. 2 shows the outline of the image output part IOT (Image Output Terminal) of an image forming apparatus according to the present embodiment. In FIG. 2, there are omitted an image read art and an image processing part. That is, there is shown only the image output part IOT of an electrophotographic type.
Here, a description will be given below of a developed image patch and its monitoring mechanism employed in the present embodiment. The developed image patch is used to monitor an output image density and, as shown in FIG. 3, as a density patch, there are employed two kinds of density patches, that is, a solid (dot coverage of 100%) density patch PA1 and a highlight (dot coverage of 20%) density patch PA2. As shown in FIG. 3, either of the solid density patch PA1 or highlight density patch PA2 is set to be of the order of 2 to 3 cm square and is formed outside the image area of the photoreceptor 2. That is, as shown in FIG. 4, after a latent image is formed in the image area 2a, the solid density patch PA1 and highlight density patch PA2 are formed sequentially in a vacant area 2b.
Also, the density sensor 10 comprises an LED radiation part for radiating light onto the surface of the photoreceptor 2, and a photosensor for receiving a regularly reflected light or a diffused light from the surface of the photoreceptor 2, while a line L1 shown in FIG. 3 is the detection line of the developed image density sensor 3. That is, the solid density patch PA1 and highlight density patch PA2 are formed on the detection line L1 and pass sequentially in the neighborhood of the developed image density sensor 10.
Next, the operation quantity means the adjustment quantities of parameters which are used to vary the output values of devices to be controlled and, in the present embodiment, the operation quantity includes two kinds of quantities, that is, the grid voltage set value (0-255, which is hereinafter abbreviated to a scoro set value) of the scorotron charger 3 and the laser power set value (0-255, which is hereinafter abbreviated to an LP set value). The reason why these two quantities are used as the operation quantity is that the final image density to be controlled includes the solid density portion and highlight density portion and also that the scoro set value and LP set value have a high correlation with the solid density and highlight density.
Also, the scoro set value and LP set value are respectively stored in an operation memory 32, while the scoro and LP set values that correspond to the output signal of an operation quantity correction value calculating unit 31 are read out from the operation quantity memory 32 as the occasion demands. The scoro set value read out from the operation quantity 32 is supplied to a grid power source 15 and, responsive to this, the grid power source 15 applies to the scorotron charger 3 a voltage corresponding to the scoro set value. Also, the LP set value read out from the operation quantity memory 32 is supplied to a light quantity controller 16 and, responsive to this, the light quantity controller 16 applies to laser output part la laser power corresponding to the LP set value.
Next, the control quantity to be supplied to the control case memory 25 is the output signal of the developed image density sensor 10 and, as a result of the above operation, in the control case memory 25, there are stored such control cases as shown in a table in FIG. 7. In this table, for example, referring to a case 1 in a cluster 1, the status quantity (occurrence time) is 951201120010 ('95, December 1, 12:00:10); the LP set value is 83; the scoro set value is 130; and, the control quantity (sensor output value) is 185 in the solid portion and 23 in the highlight portion. Also, in a case 1 in a cluster 2, the status quantity is 951202090005 ('95, December 2, 09:00:05); the LP set value is 148; the scoro set value is 115; and, the control quantity is 185 in the solid portion and 30 in the highlight portion. As will be discussed later, a control rule is formed for each cluster of control cases.
On the other hand, a reference patch signal generator 42 is a circuit which directs the formation of the solid density patch PA1 and highlight density patch PA2 and, at a patch forming timing, outputs a calibration reference patch signal to the image forming part ITO. As a result of this, the solid density patch PA1 and highlight density patch PA2 shown in FIG. 3 are formed.
When the three control cases in the initializing operation are stored in the control case memory 26, then the storage contents of the memory 26 are supplied through the status quantity comparator 26 and cluster memory 27 to the control rule calculating unit 28, where a control rule is generated. The thus generated control rule is extracted as control case planes as shown in FIG. 10 (S16). To determine the control case planes of FIG. 10, there are necessary three independent control cases. Of course, four or more control cases may also be used. In this case, a square mean error method or the like is used to determine the optimum control case planes.
In FIG. 10, P1, P2 and P3 respectively designate three points which point out three combinations of the scoro set values and LP set values in connection with the three control cases in the initializing operation. Here, points respectively indicating the highlight densities (that is, the detected densities of the highlight density patches) corresponding to the points P1, P2 and P3 are expressed as H1, H2 and H3, respectively. Similarly, points respectively representing the solid densities (the detected densities of the solid density patches) corresponding to the points P1, P2 and P3 are expressed as B1, B2 and B3, respectively. A plane passing through the three points B1, B2 and B3 is called a solid case plane BP, while a plane passing through the three points Hi, H2 and H3 is called a highlight case plane HP. Here, when the status quantity remains unchanged, points pointing out solid densities obtained when the scoro set value and LP set value are varied properly are all contained in the solid case plane BP. Similarly, when the status quantity remains unchanged, points indicating highlight densities obtained when the scoro set value and LP set value are varied properly are all contained in the highlight case plane HP. In this manner, the solid case plane BP and highlight case plane HP indicate all cases obtained when the status quantity remains unchanged. In other words, these two planes represent the control rules that relate to the solid and highlight densities in the initializing operation. These processes complete the initializing process of the present embodiment.
D100 =a1·LP+a2·SC+a3
D20=b1·LP+b2·SC+b3
SC=(b1·D100-a1·D20-a3·b1+a1·b3)/(a2.multidot.b1-a1·b2)
LP=(b2·D100-a2·D20-a3·b2+a2·b3)/(a1.multidot.b2-a2·b1)
&#916;D100=a1·&#916;LP+a2·&#916;SC
&#916;D20=b1·&#916;LP+b2·&#916;SC
&#916;SC=(b1·D100-a1·&#916;D20)/(a2·b1-a1.multidot.b2)
&#916;LP=(b2·&#916;D100-a2·&#916;D20)/(a1·b2-a2·b1)
Next, it is checked whether the density target value is changed by a user or not (S34). If not, then the latent image of the main image is formed by use of the current scoro and LP set values (S37), and the latent image is developed with a toner (S38). If the target value is found changed, then the solid density and highlight density that correspond to their respective target values are computed and differences δ D100 and δ D20 between the thus computed solid density and highlight density and the previously measured solid density and highlight density are found. The control rule that is applied to the current status is expressed by the following expressions:
By substituting previously obtained ΔD100 and ΔD20 into these expressions, ΔLP and ΔSC are obtained (S35). By subtracting thus obtained ΔLP and ΔSC from the current LP set value LP and scoro set value SC respectively, there can be obtained a new LP set value and scoro set value (S36). A latent image of the main image is formed in accordance with the newly obtained LP set value and scoro set value and the latent image is developed with a toner (S37 and S38).
w100, i=(1/E100, i)/(&#931; (1/E100, j))
w20, i=(1/E20, i)/(&#931; (1/E20, j))
where E means a sum with respect to j. Thus, the whole adaptability wi is obtained in this manner: wi=w100, i×w20, i. The sum of the adaptabilities wi is computed, and the adaptabilities of the respective control rules are divided by the thus computed sum to thereby find a normalized adaptability Wi.
FIG. 16 shows an example in which adaptabilities w100, i of solid case planes of clusters A and B are calculated. In FIG. 16, it is assumed that an actual solid patch density obtained when the current scoro and LP set values are respectively SC and LP is expressed as B0. Also, a corresponding solid patch density of the solid case plane of the cluster A and a corresponding solid patch density of the solid case plane of the cluster B are expressed as B1 and B2, respectively. Thus, deviations E100, 1 and E20, 2 are respectively |B0-B1| and |B0-B2|, respectively. Assuming that at the present time there exist only two clusters, calculation is made such that w100, 1=(1/═B0-B1|)/(1/|B0-B1|+1/|B0-B2.vertline.) and w100, 2=(1/|B0-B2|)/(1/|B0-B1|+1/|B0-B2|). Similarly, adaptabilities w100, 1 and w100, 2 of highlight densities are obtained, to thereby find the general or whole adaptabilities w1 and w2. By dividing the adaptabilities w1 and w2 by the sum (w1+w2), normalized adaptabilities W1 and W2 are obtained.
As described above, in the present embodiment, each time the status is changed, an operation to generate a new control rule suitable for the changed status starts and, if a sufficient number of cases are prepared, then a new control rule can be generated. Therefore, there is eliminated the need to collect various pieces of data to thereby cope with various conditions properly before the image forming apparatus is shipped, which makes it possible to reduce the cost of the image forming apparatus to a great extent. Also, in the present embodiment, since various kinds of control rules are synthesized together in accordance with the adaptabilities that correspond to the ever-changing conditions, it is possible to cope with various conditions even if the number of control rules is small. In this case, if control rules which correspond to typical statuses are previously input prior to the shipment of the image forming apparatus, then various statuses can be dealt with immediately. In the storage management of the control rules, if these typical control rules are previously processed in such a manner that they are not updatable, then there is no possibility that such typical control rules can be erased when a new control rule is registered.
There is obtained an error E100 between a measured solid density a target solid density. Similarly, there is obtained an error E20 between a measured highlight density and a target highlight density.
In these steps, if there occurs an outstanding case, this case is added as a case. Here, the term "outstanding case" means a case which must be taken into account in generating a new rule, or a case which must be taken into account in correcting the current control rule. In this instance, the outstanding case occurs when one of the current solid density error and the current highlight density error exceeds an allowable error. First, in Step S107, it is checked whether the current solid and highlight density errors are in the range of the allowable error. As the allowable error, the solid density is classified into 6 levels, while the highlight density is classified into 5 levels. If the density error exceeds the allowable error, then the current data and time are recorded and, after the data of the cases are stored (S108 and S109), the processing advances to a control rule generating and correcting step S110. The recording of the data on the cases will be described later in detail with reference to FIG. 19. On the other hand, if the error is in the allowable error range, then the processing advances to the control rule generating and correcting step S110 without performing any other processing.
Step Sl10!
In the control rule generating and correcting step, if the status is changed, then a new control rule is generated. On the other hand, if the status is not changed, then a control rule formed in connection with this status is corrected. Also, the adaptability on the control rule is computed. The details of the control rule generating and correcting operation will be described later with reference to FIGS. 20 and 21.
The coefficients a1, a2, b1, and b2 of all control rules Ri are multiplied by the adaptability Wi of the control rules to thereby find sums A1, A2, B1 and B2, and these sums are employed as the coefficients of an application control rule. That is, the correction values ΔSC and ΔLP of the operation quantities are found based on the deviations ΔD60 and ΔD20:
&#916;D60=A1·&#916;SC+A2·&#916;LP
&#916;D20=B1·&#916;SC+B2·&#916;LP
&#916;SC=(B2·&#916;D60-A2·&#916;D20)/(A1·B4-A2·B1)
&#916;LP=(B1·&#916;D60-A1·&#916;D20)/(A2·B1-A1·B2)
where A1=Σa1i·Wi, A2=Σa2i·Wi, B1=Σb1i·Wi, and B2=Σb2i·Wi, while Σ means a sum with respect to i.
It is checked whether a correction value can be obtained or not (S112). That is, if the value of A1·B2-A2·B1 is 0, namely, when the solid and highlight density planes of the synthesized application control rule are parallel to each other, solutions of ΔSC and ΔLP cannot be obtained; therefore, the correction value is set at 0 and the previous scoro and LP set values are used as they are (S114). On the other hand, when solutions can be obtained, ΔSC and ΔLP are found from the above expressions (S113).
If the cluster generation flag is on, it is checked whether the number of the outstanding cases stored so far is two or more, or not (S121). If the number of the cases is less than 2, then the processing goes to Step 124, in which the data on the cases are stored. If the number of the cases is two or two, then the processing goes to Step 122, in which it is checked whether a control rule can be computed or not. In the present embodiment, normally, a control rule can be generated if three cases are present. However, when the data on the three cases are arranged on a straight line, a control rule plane cannot be defined and, therefore, the control rule cannot be computed. In such a case, a new case is not stored as a normal case but is stored as a holding case (S123). The data on the holding case can be used as supplementary data when the data on a sufficient number of cases to form a control rule are prepared afterward.
Next, a description will be given below of the control rule generating/correcting operation (Sl10).
It is checked whether the cluster flag is on or not. If on, that is, if a hew control rule is to be generated, then the processing goes to Step S133. If the cluster flag is off, that is, if the previous control rule is to be corrected, then the processing advances directly to Step S137.
In this series of steps, for a plurality of control rules, their adaptabilities are obtained and an application control rule is synthesized according to the thus obtained adaptabilities. If there exists only one control rule, then the control rule, as it is, is used as an application control rule. First, the current scoro and LP set values are applied to the respective control rules to thereby compute the solid and highlight densities of the respective control rules. Then, deviations between the thus computed solid and highlight densities and the actually measured solid and highlight densities are computed (S140). The deviation between the solid densities of each control rule is expressed as E60, while the deviation between the highlight densities is expressed as E20. Next, the deviation E60 between the solid densities of each control rule is divided by the smallest solid density deviation. Similarly, the deviation E20 between the highlight densities of each control rule is divided by the smallest highlight density deviation (S141). Then, there is obtained the sum of the reciprocals of the quotients with respect to the solid density deviations, and the reciprocals of the quotients are divided by the sum, i.e., normalized. These are referred to as the contribution factors of the respective control rules with respect to the solid densities. Similarly, with respect to the highlight density deviation, there is obtained the sum of the reciprocals of the quotients, and the reciprocals of the quotients are divided by the sum, i.e., normalized. These are referred to as the contribution factors of the respective control rules with respect to the highlight densities (S142). Then, for each of control rule, the contribution factors of the solid density and the highlight density are multiplied together, and the resulting product is considered a contribution factor of the control rule (S143). Next, the contribution factor of each of control rule is divided by the largest contribution factor, and the resulting quotient is divided by the sum of the quotients, i.e., normalized (S144 and S145). The thus obtained values are stored as the adaptabilities Wi of the respective control rules Ri.
A1=&#931;wi·a1i
A2=&#931;wi&#931;a2i
B1=&#931;wi&#931;b1i
B2=&#931;wi&#931;b2i
It is checked whether a1·b2-a2·b1 is 0 or not. If it is 0, then the control planes are parallel to each other and thus the scoro and LP set values cannot be computed and, therefore, without employing the coefficients of such control rule, the control rule computation is ended.
If a1·b2-a2·b1 is not 0, then these coefficients can be employed as the coefficients of the control rule and, therefore, the write flag is switched on to thereby end the control rule coefficient computing operation.
(a) In this embodiment, by using the above-mentioned control cases, there can be realized a control method which does not use other physical quantity sensors than the density sensor and is independent of the previous data collection and the analysis thereof by engineers. This can reduce the number of sensors used and man-hours necessary for development, which in turn can reduce the manufacturing cost of the image forming apparatus. On the other hand, according to the prior art, since there is employed a control method based on a physical mechanism, when trying to perform a similar control operation to the present embodiment, physical quantities such as a charged potential, an exposure light potential and the like are monitored by a potential sensor or the like, a developed potential (a difference between the exposure light potential and a developing bias) and a cleaning potential (a difference between the charged potential and the developing bias) are obtained from the thus monitored physical quantities and the developing bias set values, the optimum developing potential for realizing the target solid density is computed according to a relationship between the previously data collected solid density and the developing potential, a variation in the highlight density caused by changing the developing potential into the optimum developing potential is computed, and a highlight density error to be corrected with the highlight density variation taken into account is computed according to a relationship between the previously data collected highlight density and the cleaning potential, thereby determining the charging potential and exposure light potential. In accordance with not only a relationship between the previously data collected charging potential and the scoro set value but also a relationship between the exposure light potential to be applied to the last-mentioned charging potential and the LP set value, LP and scoro set values to be set in the next image forming operation must be determined. Also, the previously data collection must be executed under various temperature and humidity environments since the electrophotographic system depends on the temperature and humidity.
Referring to the comparison of the above action with the prior art, for example, in a conventional control rule learning technique based on a neural network, if there are not prepared the optimum data as teachers' data, then the reasoning performance of the neural network is impaired and additional learning and re-learning cannot be carried out automatically, so that a sufficient control performance cannot be obtained. Or, in another conventional technique based on a fuzzy theory, if a trial-and-error tuning operation by an engineer is not carried out in the most suitable manner, then a sufficient control performance cannot be obtained. These comparisons show that the action of the present embodiment is fur better than the conventional techniques.
Also, according to the prior art, even the thus collected data on the changes with the passage of time cannot be always used effectively in all of image forming apparatuses because the image forming apparatuses are different from one another. Further, according to the prior art, there is left another problem to be solved: since a user uses the image forming apparatus under a different condition from the previous data collected condition by a maker, namely, since the image forming apparatus is used under such condition that is not expected by the maker, there occur such changes that are different from the maker's expected changes with the passage of time, which makes the control rule unapplicable, so that the image density cannot be controlled to a desired value. On the other hand, according to the invention, there are eliminated the previous data collection and any special means for the inter-apparatus difference, and, there can be provided an action which is able to cope with every image forming apparatus individually and perfectly under any users' environments to thereby solve the density variations caused by the changes with the passage of time.
From this action, there is also obtained another action: for example, even when element parts such as a photoreceptor, a developer and the like having significant influences on the image density are replaced, a desired image density can be automatically obtained in correspondence to the new element parts simply by executing a given number of printing operations.
A control case curved surface is able to represent a plurality of control case planes or a control case polyhedron but, to obtain the control case curved surface, a larger number of control cases are necessary and thus it takes much time to form a control rule. For example, if a solid case curved surface is expressed as a1·LP2 +a2·LP+a3·SC+4, then there are obtained coefficients a1-a4 which minimize the sum of squares of (a1·LP2 +a2·LP+a3·SC+a4-D60) with respect to the respective cases. The coefficients of the control case curved surface can be determined by use of a numerical analysis program.
As can be seen from the above description, there can be expected two kinds of control rule generating methods: in one method, a control rule is determined quickly by use of a simple plane and a large number of planes are combined together as the occasion demands; and, in the other method, from the beginning, a highly accurate control rule is expressed by a higher degree curved surface and the number of curved surfaces is reduced. Which one of the two methods is selected depends on what control characteristics are desirable to an image forming apparatus assumed or a user. The present invention can be applied to either of the two methods.
For example, it is assumed that a control rule has been existing 3 months in a similar environmental status to the status of the control rule at the time (in the season) when the control rule was extracted, and, among the control rules that have been existing three months or longer since they are formed, a control rule having the smallest cumulative adaptability is regarded as the control rule of the least importance and is thus erased. This way of erasing eliminates the possibility that only the newly extracted control rule can be erased thoughtlessly. That is, if a new control rule has been existing for 3 months or less since it was extracted, then new control rule is usually a rule of less frequency and of a small adaptability but, however, according to the above way of erasing, there is eliminated the possibility that such new control rule can be erased thoughtlessly.
(solid density)=a1×(LP set value)+a2×(scoro set value)+a3
(highlight density)=b1×(LP set value)+b2×(scoro set value)+b3
(l) In the above embodiment, the image density is the target to be controlled. However, this is not limitative but, for example, the line width, sharpness, gradation or the like may be employed as the target to be controlled.
First, a description will be given below of the background of a third embodiment of the invention. In the previously described second embodiment, the case collection time is employed as the status quantity. This is because factors that affect the status of a system to be controlled include various environmental conditions of the periphery of the system, changes with the passage of time, and the like but they can be considered almost constant in a limited range of time. For example, it can be considered that there is no substantial status changes between time points of a 20-minute interval, whereas there may occur considerable changes in temperature and humidity between morning and evening, yesterday and today, etc.
Therefore, when a control part or a system to be controlled is restarted after it was stopped, there may occur a case that the physical states of the system have changed considerably during the stop period when no control cases including status quantities are collected.
Generally speaking, such a situation can often be found in various control systems. For example, even if the external environment is constant, after a system to be controlled, which was once operated and thus the temperature thereof was raised, has been controlled under the raised temperature, in some cases, it is found that the temperature of the system is decreased down to the room temperature when it is restarted and thus the status of the system is quite different.
In such a case, in the second embodiment, if the system to be controlled is restarted and the target output of the system is designated, then the control part reads out a closest control case, that is, a control case just before a power switch is turned off, determines adaptabilities of the respective control rules from the density and operation quantity set value of the readout control case, weights and averages the respective control rules in accordance with the adaptabilities, to create (synthesize) a new control rule.
However, if the status of the system to be controlled just before the power switch is turned off is greatly different from the status after the power switch is turned off, then a control quantity obtained with respect to the previous operation quantity is quite different from the control quantity target value. That is, the adaptabilities are calculated and thus the new control rule is created based on the control case containing a great error. Of course, when the resultant control error exceeds the allowable value, as has been already described, the control accuracy in the next and its following controls can be enhanced by adding other control cases. However, if the initial error is great, then it takes much time until an allowable accuracy can be obtained.
In view of the above, according to the third embodiment, to obtain the first control case in the system restart time, an average value of an operation quantity set by a control case just before the power switch is turned off and a given standard operation quantity is calculated, and the thus calculated average value is set as the initial operation quantity. Due to this, even if the status of the system to be controlled just before the power switch is turned off is greatly different from the status of the system to be controlled when it is restarted, there can be eliminated the possibility that the initial error can be quite large.
Next, a description will be given below of the third embodiment with reference to FIGS. 26-30. In the third embodiment, the invention applied to a laser printer in which it is expected that the above-mentioned status changes at the time of a restart may occur.
Now, in FIG. 26, reference numeral 200 designates an image output part of a laser printer which part is a system to be controlled in the present embodiment. Numeral 120 stands for a control part of the laser printer which part is used to control the laser output of the image output part 200 so that a developed image density can be made to coincide with a target density.
Also, numeral 121 designates a density adjusting dial on which an operator sets a value corresponding to a desired density. The set value of the density adjusting dial 121 is converted by a converter 122 to a value (such as a value in the range of "0"-"255") which is converted to the output of a developed image density sensor 110. A target density output from the converter 122 is held in a control quantity memory 123. In this case, the control quantity memory 123 stores an allowable error as well.
On the other hand, the output signal of the developed image density sensor 110 is compared with the output signal of the control quantity memory 123 in a density comparator 124. This comparison is made with reference to the allowable error stored in the control quantity memory 123. If a difference between the output signals is within the allowable value, then the output signal of the developed image density sensor 110 is supplied to a control rule retrieval unit 130 and, if the difference is greater than the allowable value, then it is supplied to a control case memory 125. However, in the restart time of the system to be controlled which will be described later, in order to calculate the adaptabilities of the respective control rules (see the second embodiment), whether the error is large or small, the output signal of the developed image density sensor 110 is supplied to the control rule retrieval unit 130. The control quantity target value of the density is output from the density comparator 124 to the control rule retrieval unit 130. In response, the control rule retrieval unit 130 outputs the control quantity target value of the density to an operation quantity correction value calculating unit 131.
A control case memory 125 is a memory which stores a control case, in particular, which stores a set of a status quantity, an operation quantity and a control quantity. The reason why the control case is stored in the control case memory 125 is that, as described above in the second embodiment, various kinds of control can be carried out in accordance with the control cases stored in the past.
Here, the status quantity to be stored in the control case memory 125 is the values of the temperature and humidity that have the dominant effects on the electrophotographic process, the operation quantity is the set value of the laser power (which will be hereinafter referred to as an LP set value) that changes the developed image density of a laser printer, and the control quantity is the output signal of the developed density sensor 110.
A status quantity comparator 126, a cluster memory 127, and a control rule calculating unit 128 refer to the control cases stored in the control case memory 125 to thereby extract a control rule.
A control rule memory 129 is a memory which stores a plurality of control rules calculated by the control rule calculating unit 128 and, on receiving a request from the control rule retrieval unit 130, sends back a control rule corresponding to the request. In this case, the control rule retrieval unit 130 requests a control rule, which corresponds to a density difference to be supplied from the density comparator 124 and an operation quantity (that is, an LP set value) to be supplied from an operation quantity memory 132, from the control rule memory 129.
Also, the control rule retrieval unit 130, in the restart time of the system to be described later, applies an operation quantity to be supplied from the operation quantity memory 132 to the respective control rules that are stored in the control rule memory 129, and calculates the adaptabilities of the respective control rules with respect to the detection results of the developed image density sensor 110 at the then time. The control rule retrieval unit 130 uses the calculated adaptabilities as "weights" to average the respective control rules with the weights to thereby create (synthesize) a new control rule.
The operation quantity correction value calculating unit 131 calculates a correction value for the operation quantity by use of a control rule retrieved or created by the control rule retrieval unit 130, and supplies the thus-calculated correction value to the operation quantity memory 132. In response, the operation quantity memory 132 supplies an LP set value corresponding to the operation quantity correction value to a light quantity controller 116.
A standard operation quantity memory 133 is a memory which stores an operation quantity to be set when the laser printer is in a so-called standard status (for example, in a medium-temperature and medium-humidity status in which each of the temperature and humidity is neither high nor low) (which operation quantity is hereinafter referred to as a standard operation quantity). The standard operation quantity stored in the standard operation quantity memory 133, when the laser printer is restarted (for example, when a power switch is turned off once and then the power switch is turned on again), is output to the control rule retrieval unit 130. A description will be given later of the operations of the control rule retrieval unit 130 and operation quantity correction value calculating unit 131. Here, the above-mentioned control case memory 125, control rule memory 129 and standard operation quantity 133 are all formed of non-volatile memory elements. The image output part 200 includes means for detecting the on/off of the power switch and, if it detects the restart operation of the laser printer by means of the on/off of the power switch, then the image output part 100 outputs a restart detection signal to the control rule retrieval unit 130.
A reference patch signal generator 142 outputs a reference patch signal for calibration to the image output part 200. Here, the calibration reference patch signal is a signal that is output as a dummy signal to generate a patch in a given area of a photoreceptor in which an input image is not exposed, in order that the developed image density can be detected by the developed image sensor 110. The operation timing of the reference patch signal generator 142 is synchronized with the control part 120 by a synchronizing circuit 141. Also, a timer 140 is used to supply a time clock signal to the above-mentioned standard operation quantity memory 133.
Next, a description will be given below of the operation of the third embodiment having the above-mentioned structure. In the following description, as an example of the operation of the third embodiment, there is taken the operation of the laser printer when it is restarted after the power switch is turned off, in which it is assumed that the status (that is, the temperature and humidity) of the laser printer vary to a great extent.
First, after the power switch is turned off, if the power switch is turned on again and the control part 120 of the laser printer is thereby restarted, then the control rule retrieval unit 130 reads out the standard operation quantity from the standard operation quantity memory 133 and takes it in. Also, the control rule retrieval unit 130 reads out from the operation quantity memory 132 an operation quantity just before the power switch is turned off (which is referred to as "previous operation quantity"). That is, the retrieval unit 130 supplies the standard operation quantity and the previous operation quantity to the operation quantity correction value calculating unit 131. In response, the operation quantity correction value calculating unit 131 calculates an average value of the previous operation quantity and standard operation quantity that are both supplied from the control rule retrieval unit 130, and then outputs the calculated average value to the operation quantity memory 132. On receiving the average value from the operation quantity correction value calculating unit 131, the operation quantity memory 132 supplies an LP set value corresponding to the average value to the light quantity controller 116.
On the other hand, a calibration reference patch signal is output from the reference patch signal generator 142 in synchronization with the operation of the control part 120, so that a reference patch is generated in the photoreceptor. The developed image density at that time is detected by the sensor 110, and the output signal of the sensor 110 is supplied to the control rule retrieval unit 130. Responsive to this, the control rule retrieval unit 130 applies the operation quantity stored in the operation quantity memory 132 to the respective control rules and calculates the adaptabilities of the respective control rules with respect to the developed image density detected by the sensor 110, thereby creating (synthesizing) a new control rule.
Thereafter, by comparing the new control result (that is, the density difference) with the allowable error, it is judged whether the current control content should be stored additionally and, if the need arises, the control rule is corrected or a new control rule is created, thereby making preparation for the next control.
Here, with reference to FIGS. 27 to 30, a relationship between the operation quantity (LP set value) and the previous (that is, just before the power switch is turned off) control quantity (image density) obtained when the operation quantity set value ,as it is, is used as the operation quantity after the laser printer is restarted is compared with a relationship between the operation quantity (LP set value) and the previous control quantity (image density) obtained when, as in the third embodiment, the average value of the previous operation quantity set value and standard operation quantity is used as the operation quantity after the laser printer is restarted. In particular, FIG. 27 shows the former case, while FIGS. 28-30 show the latter case.
As shown in FIG. 27, in a case where the operation quantity set value "105" corresponding to the high temperature and high humidity in the previous control, as it is, is used as the operation quantity for the restart operation of the laser printer, if the status of the laser printer after it is restarted remains in the high temperature and high humidity status, then a density error is produced little but, however, if the status of the laser printer after it is restarted varies into the low temperature and low humidity status, then the density error becomes greatly large (the maximum density difference is "0.8").
On the other hand, as shown in FIG. 28, in a case where the average value "115" of the operation quantity set value corresponding to the high temperature and high humidity status in the previous control and the standard operation quantity "125" is used as the operation quantity after the restart operation of the laser printer, even if the status of the restart operation of the laser printer varies into the low temperature and low humidity status, the resultant error is not so large as in the above-mentioned case (in this case, the maximum density difference is "0.6"). Also, as shown in FIG. 29, in a case where the average value "125" of the operation quantity set value "125" corresponding to the medium temperature and medium humidity status in the previous control and the standard operation quantity "125" is used as the operation quantity of the restart operation of the laser printer, the maximum density difference is "0.4"; and, as shown in FIG. 30, in a case where the average value "135" of the operation quantity set value "145" corresponding to the low temperature and low humidity status in the previous control and the standard operation quantity "125" is used as the operation quantity of the restart operation of the laser printer, the maximum density difference is "0.6". That is, in either of the last-mentioned cases, the error is not so large as the above-mentioned first case.
As described above, according to the third embodiment, due to the fact that, in order to obtain the first control case in the restart operation of the laser printer, an average value of the standard quantity and the operation quantity set in a control case just before the power switch is turned off is calculated and the thus calculated average value is set as an initial operation quantity for the restart operation of the laser printer, even if the status of the laser printer just before the power switch is turned off differs greatly from the status in the restart operation thereof, an initial error is not large so much, which makes it possible to select and synthesize a control rule according to the proper adaptabilities, so that the restart operation of the laser printer can be controlled quickly and highly accurately from the beginning. 0158!
(a) As a modification of the third embodiment, instead of the above-mentioned standard operation quantity set value, there can be used an average value of operation quantity set values in the past control case. This eliminates the need to previously determine the standard operation quantity by means of preliminary experiments or the like. Also, when the using environment of the laser printer by a user is not a standard environment common to an ordinary user but it is a special environment peculiar to the user, the operation quantity can be determined with the user's specific using environment taken into account.
(b) As another modification of the third embodiment, instead of the average value of the previous operation quantity set value and the standard operation quantity, there can be used an average value of a value obtained by weighting the previous operation quantity set value and the standard operation quantity. In this case, the weighting is performed in accordance with the length of the stopping time of the system or the laser printer. That is, if the stopping time is short, then the weight is large. Conversely, if the stopping time is long, then the weight is small. As a result, when the stopping time is short and therefore it is probable that status variations during the stopping time are small, the average value becomes close to the set value in the previous control. On the other hand, when the stopping time is long and therefore status variations during the stopping time is unpredictable, the average value becomes close to the standard set value.
(c) Also, the above-mentioned embodiments and modifications are not limitative but other various conversion means can be employed, for example, the previous operation quantity set value may be multiplied by a given coefficient. What is important is that the previous operation quantity set value is not used as it is but some changing processing is performed on the previous operation quantity set value to thereby be able to reduce effects caused by the variations in the status of the system or the laser printer between before and after it is restarted.
(d) Further, in the present embodiment, description has been given of the restart operation of the system after the power switch is turned off. However, the invention is not limited to this but the invention can also be applied to any other kinds of restart operations of the system, provided that it can be assumed that the status of the system vary greatly.
(e) Still further, in the present embodiment, although description has been given of the control of the operation of the laser printer, this is not limitative but the invention can also be applied to the control of the operation of other systems.
As described heretofore, according to the invention, due to the fact that the transition of the status is judged and, if the status transition is found, then a new control rule is formed from new control cases, there is eliminated the need to build a complicated control system previously on the assumption of various environmental conditions. Also, since the transition of the status and the formation of the control rule are carried out in an ex post facto manner, when image forming apparatuses are different from one another in performance and history, such differences can be adapted. The present invention is able to cope automatically with a change in the performance of an image forming apparatus caused by parts replacement or by aging. Further, according to the invention, there are used a plurality of control rules, the control rules are combined together with a weight corresponding to the adaptability to thereby form an application control rule, and a control processing is carried out according to the application control rule, so that, even if each of the control rules is only able to perform a rough control processing, a fine control processing can be achieved finally.
In addition, according to the invention when a system is restarted, effects caused by variations in the status of the system between before and after the restart operation thereof can be reduced and thus the restart operation of the system can be controlled quickly and highly accurately from the beginning thereof.
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS5390004 *May 9, 1994Feb 14, 1995Xerox CorporationThree-input, three-output fuzzy logic print quality controller for an electrophotographic printerUS5400120 *Nov 13, 1992Mar 21, 1995Matsushita Electric Industrial Co., Ltd.Electrophotographic apparatusUS5483328 *Jun 10, 1994Jan 9, 1996Fujitsu, Ltd.Toner supply control system and methodUS5508787 *Apr 28, 1994Apr 16, 1996Ricoh Company, Ltd.Method and apparatus for controlling process condition for image formationUS5510896 *Jun 18, 1993Apr 23, 1996Xerox CorporationAutomatic copy quality correction and calibrationUS5528730 *Oct 2, 1990Jun 18, 1996Hitachi, Ltd.Method of control rule generation and method of fuzzy control using the same, and apparatus for automatic control rule generation and fuzzy control apparatus using the sameJPH04319971A * Title not availableJPH04320278A * Title not availableJPS63177176A * Title not availableJPS63177177A * Title not availableJPS63177178A * Title not available* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS6046820 *Oct 22, 1997Apr 4, 2000Canon Kabushiki KaishaImage forming device and computer which share the generation of a function for correcting image data based on an image forming condition of the image forming deviceUS6052195 *May 22, 1998Apr 18, 2000Xerox CorporationAutomatic colorant mixing method and apparatusUS6157469 *May 22, 1998Dec 5, 2000Xerox CorporationDynamic device independent image correction method and apparatusUS6185385 *May 22, 1998Feb 6, 2001Xerox CorporationApparatus and method for online establishment of print control parametersUS6236474May 22, 1998May 22, 2001Xerox CorporationDevice independent color controller and methodUS6344902Jan 19, 1999Feb 5, 2002Xerox CorporationApparatus and method for using feedback and feedforward in the generation of presentation images in a distributed digital image processing systemUS6377762 *Jan 30, 2001Apr 23, 2002Canon Kabushiki KaishaImage forming apparatus controlling image forming conditions based on detected toner concentration before and after stoppageUS6561098 *Dec 7, 2000May 13, 2003Heidelberger Druckmaschinen AgMethod of controlling the quantity of ink in a printing machineUS6625306Dec 7, 1999Sep 23, 2003Xerox CorporationColor gamut mapping for accurately mapping certain critical colors and corresponding transforming of nearby colors and enhancing global smoothnessUS6714319Dec 3, 1999Mar 30, 2004Xerox CorporationOn-line piecewise homeomorphism model prediction, control and calibration system for a dynamically varying color marking deviceUS6744531 *Dec 29, 1998Jun 1, 2004Xerox CorporationColor adjustment apparatus and methodUS6809837Nov 29, 1999Oct 26, 2004Xerox CorporationOn-line model prediction and calibration system for a dynamically varying color reproduction deviceUS6873432Nov 30, 1999Mar 29, 2005Xerox CorporationMethod and apparatus for representing color space transformations with a piecewise homeomorphismUS6967742 *Nov 23, 1998Nov 22, 2005Canon Kabushiki KaishaPrinter server, method for processing data and storage mediumUS7379682 *Sep 30, 2005May 27, 2008Lexmark International, Inc.Optimization of operating parameters, including imaging power, in an electrophotographic deviceUS20050134679 *Dec 4, 2003Jun 23, 2005Paterson Robert L.Margin registration of a scan line in an electrophotographic printerUS20070077081 *Sep 30, 2005Apr 5, 2007Campbell Alan SOptimization of operating parameters, including imaging power, in an electrophotographic device* Cited by examinerClassifications U.S. Classification347/133, 399/46International ClassificationG03G15/00, H04N1/407Cooperative ClassificationG03G15/5041, G03G2215/00042, H04N1/4076, H04N1/407European ClassificationG03G15/50K, H04N1/407, H04N1/407CLegal EventsDateCodeEventDescriptionMar 26, 1996ASAssignmentOwner name: FUJI XEROX CO., LTD., JAPANFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:YAMADA, KUNIO;ISHIKAWA, KIYOTAKA;REEL/FRAME:007923/0829Effective date: 19960322Sep 20, 2001FPAYFee paymentYear of fee payment: 4Sep 2, 2005FPAYFee paymentYear of fee payment: 8Nov 2, 2009REMIMaintenance fee reminder mailedMar 31, 2010LAPSLapse for failure to pay maintenance feesMay 18, 2010FPExpired due to failure to pay maintenance feeEffective date: 20100331RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services